Control apparatus for vehicular automatic transmission

ABSTRACT

Both shocks and time lag at the time of gear-in are reduced. For that purpose, the hydraulic pressure of a hydraulic engaging element to be engaged at the time of gear-in (in-gear pressure) QING is increased relatively rapidly at the beginning of gear-in. The speed of increase of QING is lowered after the input and output speed ratio &#34;Gratio&#34; of a transmission has exceeded a predetermined value YINGS which works as a basis for discriminating the start of engagement of the hydraulic engaging element.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a control apparatus for an automaticvehicular transmission having a hydraulic engaging element to be engagedat the time of gear engagement (or gear-in) by a switching operationfrom a neutral range to a running range. In this specification, the term"automatic vehicular transmission" means an automatic transmission for avehicle such as a motor vehicle.

2. Description of the Related Art

In this kind of transmission, if the pressure of hydraulic oil to besupplied to a hydraulic engaging element at the time of gear engagementor gear-in (also called an in-gear pressure) is suddenly increased atthe time of gear-in, shocks will occur. In order to alleviate this kindof shocks, it is conventionally arranged to slowly increase the in-gearpressure.

In the above-described conventional apparatus, the in-gear shocks may bealleviated, but there is a disadvantage in that the time lag between thestart of gear-in and the completion of the gear-in becomes large.

In view of the above point, the present invention has an object ofproviding a control apparatus in which the shocks and the time lag atthe time of gear-in can both be reduced.

SUMMARY OF THE INVENTION

In order to attain the above and other objects, the present invention isa control apparatus for an automatic vehicular transmission having ahydraulic engaging element to be engaged at the time of gear-in by aswitching operation from a neutral range to a running range, wherein apressure of hydraulic oil to be supplied to the hydraulic engagingelement at the time of gear-in is defined to be an in-gear pressure. Theapparatus comprises: means for detecting an input and output speed ratioof the transmission; and means for restraining boosting of the in-gearpressure after said input and output speed ratio has exceeded apredetermined value which serves as a basis for discriminating a startof engagement of said hydraulic engaging element.

In-gear shocks will occur with the rapid increase in the transmissiontorque to the driving wheels. Before the start of engagement of thehydraulic engaging element, the torque will not be transmitted to thedriving wheels. Therefore, even if the in-gear pressure is rapidlyincreased, the in-gear shocks will not occur. Further, according to thepresent invention, since an arrangement is made such that the time ofstart of the engagement of the hydraulic engaging element can bediscriminated based on the input and output gear ratio of thetransmission, the boosting of the in-gear pressure before the start ofengagement can be accelerated to thereby shorten the time lag.Thereafter, the transmission of the torque to the driving wheels isgradually increased by restraining the boosting of the in-gear pressure.The occurrence of in-gear shocks can thus be prevented.

It is also possible to completely stop the increase in the in-gearpressure by the means for restraining boosting of the in-gear pressure.This will, however, give rise to the following disadvantage. Namely, atthe time of gear-in, the input torque of the transmission normallyincreases gradually by an increase in the torque ratio due to a decreasein the speed ratio in the fluid torque converter that is interposedbetween an engine and the transmission. Therefore, if the increase inthe boosting of the in-gear pressure is completely stopped, the inputtorque balances with the capacity of the hydraulic engaging element at acertain point of time. As a result, there is a case where the hydraulicengaging element keeps on slipping and, consequently, the transmissionof the torque to the driving wheels will not proceed any further. As asolution, though the increase in the in-gear pressure keeps onincreasing, it is preferable to restrain the boosting of the in-gearpressure by lowering the speed of increase of the in-gear pressure.

Further, at a high temperature or a similar condition, the hydraulicpressure is likely to become low and, consequently, the starting ofengagement of the hydraulic engaging element is sometimes delayed. Insuch a case, if the speed of increase in the in-gear pressure after thestart of engagement is lowered in the same manner as at an ordinarytime, it takes time to the completion of the engagement, resulting in alarge time lag. Therefore, preferably, the degree of lowering of thespeed of increase of the in-gear pressure is made variable depending onthe time from the start of gear-in until the input and output speedratio has exceeded the predetermined value. In this manner, when thestarting of gear engagement is delayed, the amount of lowering of thein-gear speed is made small to thereby prevent the time lag frombecoming large.

There is a case where, while the vehicle is running, a switching is madeonce to the neutral range and then a switching is again made to therunning range, or a case where, while the vehicle is running in thereverse direction in the running range for reverse running, a switchingis made to the forward range (forward running range) via the neutralrange. At such a time, it becomes necessary to reduce the time lag ingear-in to thereby re-start the transmission of the driving force at anearly time. Here, at the time of gear-in during running, the input andoutput speed ratio of the transmission exceeds a predetermined valuefrom the beginning. Therefore, if means for restraining boosting of thein-gear pressure is operated only when the input and output speed ratiohas exceeded the predetermined value from a value smaller than thepredetermined value, the increase in the in-gear pressure is notrestrained at the time of gear-in during running. Therefore, the timelag of gear-in can advantageously be shortened to the maximum extentpossible.

In the embodiment to be described hereinafter, what corresponds to theabove-described means for restraining boosting of the in-gear pressureis the processing in steps S512 through S518 and S519 in FIG. 23. Whatcorresponds to the arrangement of lowering the speed of increase of thein-gear pressure QING is step S518. The processing in steps S517 throughS519 corresponds to the arrangement in that the degree of lowering ofthe speed of increase of the in-gear pressure is made variable dependingon the time from the start of gear-in until the input and output speedratio has exceeded the predetermined value YGINGS. Steps S512, S513 andS516 corresponds to the arrangement in that the means for restrainingboosting of the in-gear pressure is operated only when the input andoutput speed ratio has exceeded the predetermined value from a valuesmaller than the predetermined value. Further, what corresponds to theabove-described "means for detecting the input and output speed ratio"are speed sensors 23, 24 and an electronic control unit 20.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and the attendant advantages of the presentinvention will become readily apparent by reference to the followingdetailed description when considered in conjunction with theaccompanying drawings wherein:

FIG. 1 is a cross-sectional view of a transmission to which theapparatus of the present invention is applied;

FIG. 2 is a diagram showing a hydraulic oil circuit of the transmissionin FIG. 1;

FIG. 3 is an enlarged diagram of an important portion of the hydraulicoil circuit;

FIG. 4 is a block circuit diagram of a control system for solenoidvalves provided in the hydraulic oil circuit;

FIGS. 5A-5C are diagrams to show the relationship among various monitorvalues to be used in speed change control and control mode;

FIG. 6 is a time chart to show the changes in ON pressure, OFF pressure,and "Gratio" at the time of upshifting;

FIG. 7 is a flow chart to show the control at the time of upshifting;

FIG. 8 is a flow chart to show the contents of control in step S14 inFIG. 7;

FIG. 9 is a flow chart to show the contents of control in step S10 inFIG. 7;

FIG. 10 is a flow chart to show the contents of control in step S10-5 inFIG. 9;

FIG. 11 is a time chart to show the changes in ON pressure, OFFpressure, and "Gratio" at the time of downshifting;

FIG. 12 is a flow chart to show the downshifting control;

FIG. 13A is a graph to show the setting by "Gratio" of a value YGDNS fordiscriminating the speed change progress condition depending on thevehicle speed;

FIG. 13B is a graph to show the setting of YGDNS depending on the watertemperature;

FIG. 14 is a flow chart to shown the contents of control in step S108 inFIG. 12;

FIG. 15 is a time chart to show the changes in ON pressure, OFFpressure, and "Gratio" at the time of switchover upshifting;

FIG. 16 is a flow chart to show the control of switchover upshifting;

FIG. 17 is a time chart to show the changes in ON pressure, OFFpressure, and "Gratio" at the time of switchover downshifting;

FIG. 18 is a flow chart to show the control of switchover downshifting;

FIG. 19 is a flow chart to show the shift selection control;

FIG. 20A is a flow chart to show the enumeration processing of a timervalue TMG(N) to be used in the setting processing of flag FGFAIL whichis used in the control in FIG. 19;

FIG. 20B is a flow chart to show the setting processing of FGFAIL;

FIG. 21A is a graph to show the principle of setting FLOCK to be used inthe control of FIG. 19A;

FIG. 21B is a flow chart to show the setting processing of FLOCK;

FIG. 22 is a time chart to show the changes in ON pressure and "Gratio"at the time of gear-in;

FIG. 23 is a flow chart to show the in-gear control;

FIG. 24 is a flow chart to show an example of selecting processing ofspeed change map;

FIG. 25A is a flow chart to show another example of selecting processingof speed change map;

FIG. 25B is a flow chart to show the setting processing of flag FREV tobe used in the processing in FIG. 25A;

FIG. 26 is a flow chart to show the control during and afterinitialization of ECU; and

FIG. 27 is a flow chart to show the setting processing of FTBD to beused in the control in FIG. 12.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

With reference to FIG. 1, numeral 1 denotes a hydraulically operatedvehicular transmission for carrying out speed changing of four forwardtransmission trains and one reverse transmission train. The transmission1 is provided with an input shaft 3 which is connected to an engine viaa fluid torque converter 2; an intermediate shaft 5 which is alwaysconnected to the input shaft 3 via a gear train 4; and an output shaft 7having a shaft end output gear 7a which is engaged with a final gear 6aon a differential 6 which is connected to driving wheels of a vehiclesuch as a motor vehicle. In the figure, the final gear 6a and the outputgear 7a are illustrated in a manner separated from each other. This isbecause the figure is drawn in a development view, and both the gears6a, 7a are actually in mesh with each other.

A first speed transmission train G1 and a second speed transmissiontrain G2 are provided in parallel between the intermediate shaft 5 andthe output shaft 7. A third speed transmission train G3, and a fourthspeed transmission train G4 and a reverse transmission train GR areprovided in parallel between the input shaft 3 and the output shaft 7.On the intermediate shaft 5 there are provided a first speed hydraulicclutch C1 and a second speed clutch C2, which are both defined ashydraulic engaging elements, interposed in the fist speed and the secondspeed transmission trains G1, G2, respectively. On the input shaft 5there are provided a third speed hydraulic clutch C3 and a fourth speedhydraulic clutch C4, both of which are defined as hydraulic engagingelements, interposed in the third speed and the fourth speedtransmission trains G3, G4, respectively. It is thus so arranged that,when each of the hydraulic clutches C1, C2, C3, C4 is engaged, thecorresponding transmission train G1, G2, G3, G4 can be selectivelyestablished. The reverse transmission train GR is constituted orarranged to commonly use the fourth speed hydraulic clutch C4 with thefourth transmission train G4. By a switching (or changeover) operationof a selector gear 8 on the input shaft 7 between a forward running (ora forward drive) side on the left side as seen in FIG. 1 and a reverserunning (or a reverse drive) side on the right side therein, theselector gear 8 is engaged with a driven gear G4a, GRa of the fourthspeed transmission train G4 and the reverse transmission train GR,respectively. The fourth speed transmission train G4 and the reversetransmission train GR are thus selectively established. In the reversetransmission train GR, an idle gear (not illustrated) is interposed.Reference numeral 9 in the figure denotes a parking gear provided on theoutput shaft 7.

Supply and discharge of hydraulic oil to and from each of theabove-described hydraulic clutches C1-C4 are controlled by a hydrauliccircuit as shown in FIG. 2. The hydraulic circuit is provided with: ahydraulic pressure source 10 which is made up of a gear pump driven bythe engine via a casing of the fluid torque converter 2; a manual valve11 which is operated for switching in interlocking with a selector leverinside a vehicle compartment; a shift valve unit 12; a changeover valve13 on an upstream side of the shift valve unit 12; a pair of first andsecond pressure regulating valves 14₁, 14₂ which are connected to thechangeover valve 13; a servo valve 15 which switches between the forwardrunning and the reverse running and to which is connected a fork 8a tobe engaged with the selector gear 8; three sets of first through thirdsolenoid valves 16₁, 16₂, 16₃ for controlling to switch the shift valveunit 12 and the changeover valve 13; and a pair of first and secondsolenoid proportional valves 17₁, 17₂ for controlling to regulate thehydraulic pressure in the first and the second pressure regulatingvalves 14₁, 14₂. Reference numerals A1 through A4 denote accumulatorsprovided to absorb sudden pressure changes in each of the hydraulicclutches C1 through C4, respectively.

The manual valve 11 is switchable to a total of seven positions (orranges), i.e., a parking position "P", a reverse position "R", a neutralposition "N", an automatic speed changing position "D₄ " for the firstthrough the fourth speeds, an automatic speed changing position "D₃ "for the first through the third speeds, a second speed retainingposition "2", and a first speed retaining position "1".

In the "D₄ " position of the manual valve 11, No. 1 oil passage L1 whichis in communication with the hydraulic pressure source 10 is connectedto No. 2 oil passage L2 which is in communication with the changeovervalve 13. Pressurized hydraulic oil that has been regulated by aregulator 18 to a certain line pressure is supplied from No. 1 oilpassage L1 to No. 2 oil passage L2. This pressurized oil is selectivelysupplied to the first speed through the fourth speed hydraulic clutchesC1 through C4 via the changeover valve 13 and the shift valve unit 12 tothereby carry out the speed changing of the first speed through thefourth speed. Detailed explanations will be made hereinafter about theshift valve unit 12, the changeover valve 13, and the pressureregulating valves 14₁, 14₂ with reference to FIG. 3.

The shift valve unit 12 is constituted by three sets of first throughthird shift valves 12₁, 12₂, 12₃. The first shift valve 12₁ is connectedto the changeover valve 13 via two, i.e., No. 3 and No. 4, oil passagesL3, L4. The second shift valve 12₂ is connected to the changeover valve13 via two, i.e., No. 5 and No. 6, oil passages L5, L6. The first andthe second shift valves 12₁, 12₂ are connected to each other via three,i.e., No. 7 through No. 9, oil passages L7, L8, L9. Further, the thirdshift valve 12₃ is connected to the first shift valve 12₁ via two, i.e.,No. 10 and No. 11, oil passages L10, L11 and is also connected to thesecond shift valve 12₂ via No. 12 oil passage L12.

The first speed hydraulic clutch C1 is connected to the second shiftvalve 12₂ via No. 13 oil passage L13. The second speed hydraulic clutchC2 is connected to the first shift valve 12₁ via No. 14 oil passage L14.The third speed hydraulic clutch C3 is connected to the second shiftvalve 12₂ via No. 15 oil passage L15. The fourth speed hydraulic clutchC4 is connected to the first shift valve 12₁ via No. 17 oil passage L17which is connected, in the "D₄ ", "D₃ ", "2" and "1" positions of themanual valve 11, to No. 16 oil passage L16 that is connected to thefourth speed hydraulic clutch C4.

The first shift valve 12₁ is urged to the right position by a spring 12₁a and is also urged to the left position by the hydraulic pressure inNo. 18 oil passage L18 which is controlled by the first solenoid valve16₁. The second shift valve 12₂ is urged to the right position by aspring 12₂ a and is also urged to the left position by the hydraulicpressure in No. 19 oil passage L19 which is controlled by the secondsolenoid valve 16₂. The third shift valve 12₃ is urged to the right by aspring 12₃ a and is also urged to the left by the hydraulic pressure inNo. 21 oil passage L21 which is connected to No. 1 oil passage L1 in aposition of the manual valve 11 other than the "2" and "1" positions. Inthe "D₄ " position of the manual valve 11, the third shift valve 12₃ isheld or retained in the left position by the line pressure to beinputted via No. 21 oil passage L21 so that No. 10 oil passage L10 isconnected to an oil discharge port 12₃ b of the third shift valve 12₃,and No. 11 oil passage L11 and No. 12 oil passage L12 are connectedtogether.

At the time of the first speed running (or the first speed drive) in the"D₄ " position of the manual valve 11, the first shift valve 12₁ isswitched to the left position and the second shift valve 12₂ is switchedto the right position. According to these operations, No. 13 oil passageL13 for the first speed hydraulic clutch C1 is connected to No. 4 oilpassage L4 which is defined as a second connecting oil passage to thechangeover valve 13. At this time, No. 14 oil passage L14 for the secondspeed hydraulic clutch C2 is connected to that oil discharge port 12₃ bof the third shift valve 12₃ which is defined as an oil dischargepassage, via the first shift valve 12₁ and No. 10 oil passage L10. No.15 oil passage L15 for the third speed hydraulic clutch C3 is connectedto that oil discharge port 12₂ b of the second shift valve 12₂ which isdefined as an oil discharge passage. No. 16 oil passage L16 for thefourth speed hydraulic clutch C4 is connected to No. 6 oil passage L6,which is defined as a fourth connecting oil passage to the changeovervalve 13, via No. 17 oil passage L17, the first shift valve 12₁, No. 11oil passage L11, the third shift valve 12₃, No. 12 oil passage L12, andthe second shift valve 12₂.

At the time of the second speed running, the first shift valve 12₁ isswitched to the right position while holding the second shift valve 12₂in the right position. According to these operations, No. 14 oil passageL14 for the second speed hydraulic clutch C2 is connected to No. 5 oilpassage L5, which is defined as a third connecting oil passage to thechangeover valve 13, via the first shift valve 12₁, No. 9 oil passageL9, and the second shift valve 12₂. No. 13 oil passage L13 for the firstspeed hydraulic clutch C1 is connected to No. 3 oil passage L3, which isdefined as a first connecting oil passage to the changeover valve 13,via the second shift valve 12₂, No. 8 oil passage L8, and the firstshift valve 12₁. At this time, No. 15 oil passage L15 for the thirdspeed hydraulic clutch C3 is connected to the oil discharge port 12₂ bof the second shift valve 12₂ like at the time of the first speedrunning. No. 16 oil passage L16 for the fourth speed hydraulic clutch C4is connected to that oil discharge port 12₁ b of the first shift valve12₁ which is defined as a discharge oil passage, via No. 17 oil passageL17.

At the time of the third speed running, the second shift valve 12₂ isswitched to the left position while holding the first shift valve 12₁ inthe right position. According to these operations, No. 15 oil passageL15 for the third speed hydraulic clutch C3 is connected to No. 4 oilpassage L4 via the second shift valve 12₂, No. 7 oil passage L7 and thefirst shift valve 12₁. No. 14 oil passage L14 for the second speedhydraulic clutch C2 is connected to No. 6 oil passage L6 via the firstshift valve 12₁, No. 9 oil passage L9 and the second shift valve 12₂. Atthis time, No. 13 oil passage L13 for the first speed hydraulic clutchC1 is connected to the oil discharge port 12₂ b of the second shiftvalve 12₂. No. 16 oil passage L16 for the fourth hydraulic clutch C4 isconnected to the oil discharge port 12₁ b of the first shift valve 12₁via No. 17 oil passage L17, like at the time of the second speedrunning.

At the time of the fourth speed running, the first shift valve 12₁ isswitched to the left position while holding the second shift valve 12₂in the left position. According to these operations, No. 16 oil passageL16 for the fourth speed hydraulic clutch C4 is connected to No. 5 oilpassage L5 via No. 17 oil passage L17, the first shift valve 12₁, No. 11oil passage L11, the third shift valve 12₃, No. 12 oil passage L12 andthe second shift valve 12₂. No. 15 oil passage L15 for the third speedhydraulic clutch C3 is connected to No. 3 oil passage L3 via the secondshift valve 12₂, No. 7 oil passage L7 and the first shift valve 12₁. Atthis time, No. 13 oil passage L13 for the first speed hydraulic clutchC1 is connected to the oil discharge port 12₂ b of the second shiftvalve 12₂, like at the time of the third speed running. No. 14 oilpassage L14 for the second speed hydraulic clutch C2 is connected to theoil discharge port 12₃ b of the third shift valve 12₃ via the firstshift valve 12₁ and No. 10 oil passage L10, like at the time of thefirst speed running.

To the changeover valve 13 there are connected: No. 2 oil passage L2which is defined as an oil passage at a line pressure; No. 3 through No.6 oil passages L3, L4, L5, L6 as the first through the fourth connectingoil passages; No. 22 oil passage L22 which is defined as a firstpressure-regulated oil passage whose pressure is regulated by the firstpressure regulating valve 14₁ ; and No. 23 oil passage L23 which isdefined as a second pressure-regulated oil passage whose pressure isregulated by the second pressure regulating valve 14₂. The changeovervalve 13 is urged to the right position, which is defined as a firstswitchover position, by a predetermined pressure lower than the linepressure (hereinafter called a modulator pressure) which is outputted toNo. 24 oil passage L24 on the downstream side of a modulator valve 19which is connected to No. 1 oil passage L1. The changeover valve 13 isurged to the left position, which is defined as a second switchoverposition, by a spring 13a and the hydraulic pressure in No. 20 oilpassage L20 to be controlled by the third solenoid valve 16₃.

When the changeover valve 13 is in the right position, No. 3 oil passageL3 is connected to No. 22 oil passage L22, and No. 5 oil passage L5 isconnected to No. 23 oil passage L23. Therefore, it becomes possible toregulate the hydraulic pressure in each of No. 3 and No. 5 oil passagesL3, L5 by the first and the second pressure regulating valves 14₁, 14₂,respectively. At this time, No. 4 oil passage L4 is connected to No. 2oil passage L2, and No. 6 oil passage L6 is connected to that oildischarge port 13b of the changeover valve 13 which is defined as an oildischarge passage.

When the changeover valve 13 is in the left position, No. 4 oil passageL4 is connected to No. 22 oil passage L22, and No. 6 oil passage L6 isconnected to No. 23 oil passage L23. Therefore, it becomes possible toregulate the hydraulic pressure in each of No. 4 and No. 6 oil passagesL4, L6 by the first and the second pressure regulating valves 14₁, 14₂,respectively. At this time, No. 3 oil passage L3 is connected to thatoil discharge port 13c of the changeover valve 13 which is defined asthe oil discharge passage, and No. 5 oil passage L5 is connected to No.2 oil passage L2.

At the time of the first speed in which the first shift valve 12₁ is inthe left position, the second shift valve 12₂ is in the right position,and the first speed hydraulic clutch C1 is connected to No. 4 oilpassage L4, the changeover valve 13 is switched and held in the rightposition, and No. 4 oil passage L4 is connected to No. 2 oil passage L2.In this way, the hydraulic pressure in the first speed hydraulic clutchC1 (hereinafter called a first speed pressure) becomes the linepressure, whereby the first speed transmission train G1 is establishedthrough the engagement of the first speed hydraulic clutch C1.

At the time of the second speed in which both the first and the secondshift valves 12₁, 12₂ are in the right position, and the first speedhydraulic clutch C1 is connected to No. 3 oil passage L3, and the secondspeed hydraulic clutch C2 is connected to No. 5 oil passage L5,respectively, the changeover valve 13 is switched and held in the leftposition, No. 3 oil passage L3 is connected to the oil discharge port13c, and No. 5 oil passage L5 is connected to No. 2 oil passage L2. Inthis manner, the first speed pressure is lowered to the atmosphericpressure to thereby release the engagement of the first speed hydraulicclutch C1. On the other hand, the hydraulic pressure in the second speedhydraulic clutch C2 (hereinafter called a second speed pressure) becomesthe line pressure, whereby the second speed transmission train G2 isestablished through the engagement of the second speed hydraulic clutchC2.

At the time of upshifting from the first speed to the second speed, boththe first and the second shift valves 12₁, 12₂ are first switched to thecondition of the second speed while holding the changeover valve 13 inthe position at the time of the first speed, i.e., in the rightposition. In this case, No. 3 and No. 5 oil passages L3, L5 to beconnected to the first and the second speed hydraulic clutches C1, C2,respectively, are connected to No. 22 and No. 23 oil passages L22, L23,respectively. Therefore, it becomes possible to control the pressuredrop characteristics of the first speed pressure by the first pressureregulating valve 14₁ and to control the pressure rise characteristics ofthe second speed pressure by the second pressure regulating valve 14₂,whereby a smooth upshifting from the first speed to the second speed canbe carried out. After the speed changing has been completed, thechangeover valve 13 is switched to the left position. Hydraulic oil isdischarged from the first speed hydraulic clutch C1 without passingthrough the first pressure regulating valve 14₁, and the second speedhydraulic clutch C2 is supplied with pressurized oil at the linepressure without passing through the second pressure regulating valve14₂.

At the time of downshifting from the second speed to the first speed,the changeover valve 13 is first switched from the position at the timeof the second speed to the position at the time of the first speed,i.e., from the left position to the right position, while holding boththe shift valves 12₁, 12₂ to the condition at the time of the secondspeed. According to these operations, like at the time of upshiftingfrom the first speed to the second speed, both the first speed and thesecond speed hydraulic clutches C1, C2 are connected to No. 22 and No.23 oil passages L22, L23, respectively. Therefore, it becomes possibleto control the pressure rise characteristics of the first speed pressureby the first pressure regulating valve 14₁, and to control the pressuredrop characteristics of the second speed pressure by the second pressureregulating valve 14₂, whereby a smooth downshifting from the secondspeed to the first speed can be carried out. After the speed changinghas been completed, both the first and the second shift valves 12₁, 12₂are switched to the condition of the first speed running. The secondspeed hydraulic clutch C2 is connected to the oil discharge port 12₃ bof the third shift valve 12₃. The hydraulic oil is thus discharged fromthe second speed hydraulic clutch C2 without passing through the secondpressure regulating valve 14₂. And the first speed hydraulic clutch C1is supplied with the pressurized oil at the line pressure withoutpassing through the first pressure regulating valve 14₁ like at the timeof the first speed.

At the time of the third speed in which the first shift valve 12₁ is inthe right position, the second shift valve 12₂ is in the left position,the second speed hydraulic clutch C2 is connected to No. 6 oil passageL6, and the third speed hydraulic clutch C3 is connected to No. 4 oilpassage L4, respectively, the changeover valve 13 is switched and heldin the right position. Like at the time of the first speed running, No.6 oil passage L6 is connected to the oil discharge port 13b and No. 4oil passage L4 is connected to No. 2 oil passage L2. In this manner, thesecond speed pressure is lowered to the atmospheric pressure and theengagement of the second speed hydraulic clutch C2 is thereby released.On the other hand, the hydraulic pressure in the third speed hydraulicclutch C3 (hereinafter called a third speed pressure) becomes the linepressure, whereby the third speed transmission train G3 is establishedthrough the engagement of the third speed hydraulic clutch C3.

At the time of upshifting from the second speed to the third speed, boththe first and the second shift valves 12₁, 12₂ are switched to thecondition of the third speed while holding the changeover valve 13 inthe position of the second speed running, i.e., in the left position. Inthis case, No. 4 and No. 6 oil passages L4, L6 to be connected to thethird and the second speed hydraulic clutches C3, C2 are connected toNo. 22 and No. 23 oil passages L22, L23, respectively. Therefore, itbecomes possible to control the pressure rise characteristics of thethird speed pressure by the first pressure regulating valve 14₁ and tocontrol the pressure drop characteristics of the second speed pressureby the second pressure regulating valve 14₂. Therefore, a smoothupshifting from the second speed to the third speed can be carried out.After the speed changing has been completed, the changeover valve 13 isswitched to the right position. The hydraulic oil is discharged from thesecond speed hydraulic clutch C2 without passing through the secondpressure regulating valve 14₂, and the third speed hydraulic clutch C3is supplied with the pressurized oil at the line pressure withoutpassing through the first pressure regulating valve 14₁.

At the time of downshifting from the third speed to the second speed,the changeover valve 13 is first switched from the position at the timeof the third speed to the position at the time of second speed, i.e.,from the right position to the left position, while holding both thefirst and the second shift valves 12₁, 12₂ to the condition of the thirdspeed. According to these operations, like at the time of upshiftingfrom the second speed to the third speed, both the third speed and thesecond speed hydraulic clutches C3, C2 are connected to No. 22 and No.23 oil passages L22, L23, respectively. Therefore, it becomes possibleto control the pressure drop characteristics of the third speed pressureby the first pressure regulating valve 14₁, and to control the pressurerise characteristics of the second speed pressure by the second pressureregulating valve 14₂, whereby a smooth downshifting from the third speedto the second speed can be carried out. After the speed changing hasbeen completed, both the fist and the second shift valves 12₁, 12₂ areswitched to the condition of the second speed and the third speedhydraulic clutch C3 is connected to the oil discharge port 12₂ b of thesecond shift valve 12₂. The hydraulic oil is thus discharged from thethird speed hydraulic clutch C3 without passing through the firstpressure regulating valve 14₁ and the second speed hydraulic clutch C2is supplied with the pressurized oil at the line pressure withoutpassing through the second pressure regulating valve 14₂ like at thetime of the second speed.

At the time of the fourth speed in which both the first and the secondshift valves 12₁, 12₂ are in the left position, and the third speedhydraulic clutch C3 is connected to No. 3 oil passage L3, and the fourthspeed hydraulic clutch C4 is connected to No. 5 oil passage L5,respectively, the changeover valve 13 is switched and held at the leftposition. Like at the time of second speed, No. 3 oil passage L3 isconnected to the oil discharge port 13c, and No. 5 oil passage L5 isconnected to No. 2 oil passage L2. In this manner, the third speedpressure is lowered to the atmospheric pressure to thereby release theengagement of the third speed hydraulic clutch C3. On the other hand,the hydraulic pressure in the fourth speed hydraulic clutch C4(hereinafter called a fourth speed pressure) becomes the line pressure,whereby the fourth speed transmission train G4 is established throughthe engagement of the fourth speed hydraulic clutch C4.

At the time of upshifting from the third speed to the fourth speed, boththe first and the second shift valves 12₁, 12₂ are switched to thecondition of the fourth speed while holding the changeover valve 13 inthe position of the third speed, i.e., in the right position. In thiscase, No. 3 and No. 5 oil passages L3, L5 to be connected to the thirdand the fourth hydraulic clutches C3, C4 are connected to No. 22 and No.23 oil passages L22, L23, respectively. Therefore, it becomes possibleto control the pressure drop characteristics of the third speed pressureby the first pressure regulating valve 14₁ and to control the pressurerise characteristics of the fourth speed pressure by the secondregulating valve 14₂. A smooth upshifting from the third speed to thefourth speed can thus be carried out. After the speed changing has beencompleted, the changeover valve 13 is switched to the left position. Thehydraulic oil is discharged from the third speed hydraulic clutch C3without passing through the first pressure regulating valve 14₁. And thefourth speed hydraulic clutch C4 is supplied with the oil at the linepressure without passing through the second pressure regulating valve14₂.

At the time of downshifting from the fourth speed to the third speed,the changeover valve 13 is first switched from the position at the timeof the fourth speed to the position at the time of the third speed,i.e., from the left position to the right position, while holding boththe first and the second shift valves 12₁, 12₂ to the condition of thefourth speed. According to these operations, like at the time ofupshifting from the third speed to the fourth speed, the third speed andthe fourth speed hydraulic clutches C3, C4 are connected to No. 22 andNo. 23 oil passages L22, L23, respectively. Therefore, it becomespossible to control the pressure rise characteristics of the third speedpressure by the first pressure regulating valve 14₁, and to control thepressure drop characteristics of the fourth speed pressure by the secondpressure regulating valve 14₂, whereby a smooth downshifting from thefourth speed to the third speed can be carried out. After the speedchanging has been completed, both the fist and the second shift valves12₁, 12₂ are switched to the condition of the third speed. The fourthspeed hydraulic clutch C4 is connected to the oil discharge port 12₁ bof the first shift valve 12₁. The hydraulic oil is thus discharged fromthe fourth speed hydraulic clutch C4 without passing through the secondpressure regulating valve 14₂. And the third speed hydraulic clutch C3is supplied with the pressurized oil at the line pressure withoutpassing through the first pressure regulating valve 14₁.

Each of the first and the second pressure regulating valves 14₁, 14₂ isurged by each of springs 14₁ a, 14₂ a and by the hydraulic pressure ineach of No. 22 and No. 23 oil passages L22, L23 to the rightward oildischarge side in which each of No. 22 and No. 23 oil passages L22, L23is connected to each of the oil discharge ports 14₁ b, 14₂ b,respectively. Further, the first and the second pressure regulatingvalves 14₁, 14₂ are urged by the respective hydraulic pressures in No.25 and No. 26 oil passages L25, L26 on the output side of each ofsolenoid proportional valves 17₁, 17₂ to the leftward oil supply side inwhich No. 22 and No. 23 oil passages L22, L23 are respectively connectedto No. 2 oil passages L2. In this manner, the hydraulic pressure in eachof No. 22 and No. 23 oil passages L22, L23 is increased or decreased inproportion to the output pressure of each of the solenoid proportionalvalves 17₁, 17₂. In order to decrease the speed change shocks, itbecomes necessary to perform a delicate control of the hydraulicpressure in a transient region of engagement of the hydraulic clutch onthe disengaging side and the hydraulic clutch on the engaging side. Inthis embodiment, after the completion of the speed changing, thehydraulic oil supply to the hydraulic clutch on the engaging side andthe hydraulic oil discharge from the hydraulic clutch on the disengagingside are made without passing through the pressure regulating valves14₁, 14₂. Therefore, the pressure regulating valves 14₁, 14₂ need tobear the hydraulic pressure control only in the transient region ofengagement at a relatively low hydraulic pressure. Therefore, theresolution of the pressure control can be made higher and the delicatecontrol of the pressure rise characteristics of the hydraulic clutch onthe engaging side and the pressure drop characteristics of the hydraulicclutch on the disengaging side can be performed at a higher accuracy.

Modulator pressure is inputted into both the first and the secondsolenoid proportional valves 17₁, 17₂ via No. 24 oil passage L24. Here,as the first solenoid proportional valve 17₁, there is used one in whichan output pressure becomes maximum (modulator pressure) at the time ofnon-energization. As the second solenoid proportional valve 17₂, thereis used one in which the output pressure becomes minimum (atmosphericpressure) at the time of non-energization.

The first solenoid valve 16₁ is constituted by a two-way valve whichopens to atmosphere No. 18 oil passage L18 which is connected to No. 24oil passage L24 via a throttle 16₁ a. At the time of non-energizationthereof, it is closed to thereby change the hydraulic pressure in No. 18oil passage L18 to a high hydraulic pressure (modulator pressure).

Each of the second and the third solenoid valves 16₂, 16₃ is constitutedby a three-way valve which is switchable between an oil supply positionin which No. 19 and No. 20 oil passages L19, L20 on the output side ofthe respective solenoid valves are connected to No. 24 oil passage L24,and an oil discharge position in which this connection is shut off andconnect each of the oil passages L19, L20 to each of oil discharge ports162a, 163a, respectively. At the time of non-energization thereof, it isswitched to the oil supply position and change the hydraulic pressure ineach of No. 19 and No. 20 oil passages L19, L20 to a high hydraulicpressure (modulator pressure).

It may also be considered to constitute the second and the thirdsolenoid valves 16₂, 16₃ by a two-way valve like the first solenoidvalve 16₁. However, the two-way valve has disadvantages in that an oilleak amount when opened becomes large and that the control responsebecomes poor because, at a low temperature, there remains a residualhydraulic pressure even when it is opened. Here, at the time of lowspeed running at the first speed or at the time when the vehicle isstopped, the revolution speed of the engine lowers so that the amount ofoil supply from the hydraulic pressure source 10 decreases and,therefore, the oil leak amount must be minimized. In addition, at thefirst speed, since the second shift valve 12₂ and the changeover valve13 are moved to the right position, No. 19 and No. 20 oil passages L19,L20 must be made to the atmospheric pressure. If the second and thethird solenoid valves 16₂, 16₃ are constituted by two-way valves, theleak amount becomes excessive. In view of the above disadvantages and inview of the fact that the switching operation of the changeover valve 13that must be switched with a good response is carried out by the thirdsolenoid valve 16₃, the following arrangement has been employed in thisembodiment. Namely, the second and the third solenoid vales 16₂, 16₃ arerespectively constituted by a three-way valve and, in view of the space,only the first solenoid valve 16₁ is constituted by a small-sizedtwo-way valve.

In the "D₄ " position of the manual valve 11, the state of energizationor non-energization of the first through the third solenoid valves 16₁,16₂, 16₃ ; the position of the first and the second shift valves 12₁,12₂ ; and the output pressures (pressures in No. 22 and No. 23 oilpassages L22, L23) of the first and the second pressure regulatingvalves 14₁, 14₂ ; at the in-gear time (initial gear engagement), as wellas at the first through the fourth speeds are as shown in the tablegiven hereinbelow.

    __________________________________________________________________________               ##STR1##                                                                         ##STR2##                                                                           ##STR3##                                                                         ##STR4##                                                                           ##STR5##                                                                          ##STR6##                                                                           ##STR7##                                  __________________________________________________________________________    1st sol. valve (16.sub.1)                                                               X  O    O  O    O   X    X                                          2nd sol. valve (16.sub.2)                                                               O  O    O  X    X   X    X                                          3rd sol. valve (16.sub.3)                                                               O  O    X  X    O   O    X                                          1st shift valve (12.sub.1)                                                              Left                                                                             Right                                                                              Right                                                                            Right                                                                              Right                                                                             Left Left                                       2nd shift valve (12.sub.2)                                                              Right                                                                            Right                                                                              Right                                                                            Left Left                                                                              Left Left                                       changeover valve (13)                                                                   Right                                                                            Right                                                                              Left                                                                             Left Right                                                                             Right                                                                              Left                                       1st p. reg. valve (14.sub.1)                                                            H  H   L                                                                              L  L  H H   H   L                                                                              L                                          2nd p. reg. valve (14.sub.2)                                                            L  L   H                                                                              H  H   L                                                                              L   L   H                                                                              H                                          __________________________________________________________________________     sol. valve = solenoid valve;                                                  p reg. valve = pressure regulating valve;                                     L = Low;                                                                      H = High;                                                                     O = energized;                                                                X = not energized                                                        

In this embodiment, between the first and the second pressure regulatingvalves 14₁, 14₂, the one that functioned as an oil supply pressureregulating valve for boosting the hydraulic pressure in the hydraulicclutch on the engaging side at the time of the last speed changing willfunction as an oil discharge pressure regulating valve (i.e., a pressureregulating valve for oil discharge) for dropping or lowering thehydraulic pressure in the hydraulic clutch on the disengaging side atthe time of the next speed changing. Further, the one that functioned asan oil discharge pressure regulating valve at the time of the last speedchanging will function as an oil supply pressure regulating valve (i.e.,a pressure regulating valve for oil supply) at the time of the nextspeed changing. Therefore, the output pressure of each of the pressureregulating valves 14₁, 14₂ can be maintained as it is to thereby make itready for the next speed changing. On the contrary, if one of the firstand the second pressure regulating valves 14₁, 14₂ is used exclusivelyfor oil supply and the other thereof is used exclusively for oildischarge, the following becomes necessary. Namely, the output pressureof the oil supply pressure regulating valve that was boosted at the timeof speed changing must be lowered, and also the output pressure of theoil discharge pressure regulating valve that was lowered at the time ofspeed changing must be boosted to be prepared for the next speedchanging. In this case, if the next speed changing is made at a lowtemperature within a short period of time, the speed changing will startwhen the pressure dropping of the output pressure in the oil supplypressure regulating valve or the boosting of the output pressure in theoil discharge pressure regulating valve has not been made sufficiently.As a consequence, the hydraulic pressure control at the time of speedchanging gets out of order and the speed change shocks are likely tooccur. Therefore, it is preferable to use, as in this embodiment, thefirst and the second pressure regulating valves 14₁, 14₂ alternately foroil supplying and for oil discharging at each speed changing.

The first through the third solenoid valves 16₁, 16₂, 16₃ as well as thefirst and the second solenoid proportional valves 17₁, 17₂ arecontrolled, together with a fourth solenoid valve 16₄ for a lockupclutch which is described later, by an electronic control unit 20 whichis made up of a microcomputer as shown in FIG. 4.

In the electronic control unit (ECU) 20, there are inputted: a signalfrom a throttle sensor 21 for detecting a throttle opening θ of theengine; a signal from a vehicle speed sensor 22 for detecting thevehicle speed V; a signal from a speed sensor 23 for detecting therotational speed Nin of the input shaft 3 of the transmission; a signalfrom a speed sensor 24 for detecting the rotational speed Nout of theoutput shaft 7 of the transmission; and a signal from a position sensor25 for the selector lever.

In the "D₄ " position, a transmission train that suits the presentthrottle opening θ and the vehicle speed V is selected based on a speedchange map for the first through the fourth speeds kept in memory in theECU 20, thereby carrying out an automatic speed changing of the firstthrough the fourth speeds.

Also in the "D₃ " position, the same oil circuit arrangement applies asthat in the "D₄ " position. Automatic speed changing of the firstthrough the third speeds is performed based on the speed change map forthe first through the third speeds that is stored in the ECU 20.

In the "2" and "1" positions, a stepwise downshifting to the secondspeed or to the first speed is carried out based on the second speed mapor the first speed map that is stored in the ECU 20. Thereafter, thespeed is maintained in the second speed or the first speed. In the "2"and "1" positions, No. 21 oil passage L21 that was connected to No. 1oil passage L1 is opened to atmosphere. The third shift valve 12₃ canthus become switchable to the right position.

When the third shift valve 12₃ is switched to the right position, No. 10oil passage L10 that was connected, in the left position, to the oildischarge port 12₃ b is connected to No. 12 oil passage L12. And No. 11oil passage L11 that was connected, in the left position, to No. 12 oilpassage L12 is connected to the oil discharge port 12₃ c of the thirdshift valve 12₃. No. 10 oil passage L10 and No. 11 oil passage L11 areconnected, in the right position of the first shift valve 12₁, to noneof the oil passages for the hydraulic clutches. When the first shiftvalve 12₁ is moved to the right position, the oil circuit arrangementwill become the same as that when the first shift valve 12₁ is moved tothe right position in the "D₄ " position. Therefore, when both the firstand the second shift valves 12₁, 12₂ are switched to the right position(a condition of the second speed in the "D₄ " position), the hydraulicoil is supplied to the second speed hydraulic clutch C2 to therebyestablish the second speed transmission train G2. When the first shiftvalve 12₁ is moved to the right position and the second shift valve 12₂is moved to the left position (a condition of the third speed in the "D₃position), the hydraulic oil is supplied to the third speed hydraulicclutch C3 to thereby establish the third speed transmission train G3.

On the other hand, when the first shift valve 12₁ is switched to theleft position, No. 14 oil passage L14 for the second speed hydraulicclutch C2 is connected to No. 10 oil passage L10, and No. 17 oil passageL17 for the fourth speed hydraulic clutch C4 is connected to No. 11 oilpassage L11, respectively, the oil circuit arrangement will thereforebecome different from that in the "D₄ " position. When the first shiftvalve 12₁ is moved to the left position and the second shift valve 12₂is moved to the right position (a condition of the first speed in the"D₄ " position), No. 13 oil passage L13 for the first speed hydraulicclutch C1 is connected to No. 4 oil passage L4 (this connection is thesame as that in the "D₄ " position), and No. 14 oil passage L14 for thesecond speed hydraulic clutch C2 is connected to No. 6 oil passage L6(in the "D₄ " position No. 17 oil passage L17 for the fourth speedhydraulic clutch C4 is connected to No. 6 oil passage L6). When both thefirst and the second shift valves 12₁, 12₂ are moved to the leftposition (a condition of the fourth speed in the "D₄ " position), No. 15oil passage L15 for the third speed hydraulic clutch C3 is connected toNo. 3 oil passage L3 (this connection is the same as that in the "D₄ "position). No. 14 oil passage L14 for the second speed hydraulic clutchC2 is connected to No. 5 oil passage L5 (in the "D₄ " position No. 17oil passage L17 for the fourth speed hydraulic clutch C4 is connected toNo. 5 oil passage L5). No oil supply is therefore made to the fourthspeed hydraulic clutch C4.

Here, the third shift valve 12₃ is arranged to be urged to the left bythat output pressure of the second solenoid proportional valve 17₂ whichis inputted via No. 26 oil passage L26. However, when the electric powersupply to the first through the third solenoid valves 16₁, 16₂, 16₃ aswell as to the first and the second solenoid proportional valves 17₁,17₂ stops at the time of a system failure due to opening of a fuse orthe like, both the first and the second shift valves 12₁, 12₂ and thechangeover valve 13 are switched to the left position, and also theoutput pressure of the second solenoid proportional valve 17₂ becomesthe atmospheric pressure. The third shift valve 12₃ is thus switched inthe "2" and the "1" positions to the right position and switched, in the"D₄ " and the "D₃ " positions, to the left position by the line pressurefrom No. 21 oil passage L21. Therefore, in the "1" and the "2"positions, the second speed transmission train G2 is established and, inthe "D₄ " and the "D₃ " positions, the fourth speed transmission trainG4 is established, respectively. The vehicle is able to run at thesecond speed and the fourth speed even at the time of the systemfailure.

In the "R" position of the manual valve 11, No. 2 oil passage L2 isopened to the atmosphere. No. 27 oil passage L27 is connected to No. 1oil passage L1 and the hydraulic oil is supplied to a first oil chamber15a on the left end of the servo valve 15 via No. 28 oil passage L28which is connected to No. 27 oil passage L27 via a first servo controlvalve 27. According to these operations, the servo valve 15 is urged tothe rightward reverse running position to thereby switch the selectorgear 8 to the reverse running side. Also No. 28 oil passage L28 isconnected to No. 29 oil passage L29 via that shaft bore 15b of the servovalve 15 which is communicated with the first oil chamber 15a. The oilpassage L29 is connected to No. 16 oil passage L16 which is communicatedwith the fourth speed hydraulic clutch C4 in the "R" position of themanual valve 11. In this manner, the reverse transmission train GR isestablished by the hydraulic oil supply to the fourth speed hydraulicclutch C4 and by the switching of the selector gear 8 to the reverserunning side.

The first servo control valve 27 is urged, by the hydraulic pressure inNo. 20 oil passage L20 on the output side of the third solenoid valve163 and the hydraulic pressure in No. 25 oil passage L25 on the outputside of the first solenoid proportional valve 17₁, to the leftward openside in which No. 27 oil passage L27 and No. 28 oil passage L28 areconnected. It is urged by a spring 27a, the hydraulic pressure in No. 2oil passage L2 and the hydraulic pressure in No. 29 oil passage L29, tothe rightward closed side in which the connection between No. 27 oilpassage L27 and No. 28 oil passage L28 is shut off and connect No. 28oil passage L28 to an oil discharge port 27b. In the "D₄ ", "D₃ ", "2"or "1" position, by means of the line pressure to be inputted via No. 2oil passage L2, the first servo control valve 27 is held in the rightposition even if the output pressures of the third solenoid valve 16₃and the first solenoid proportional valve 17₁ may both be increased. Theoil supply to No. 28 oil passage L28 is thus blocked, and the servovalve 15 is retained in the leftward forward running position by anengaging member 15c, whereby the establishment of the reversetransmission train GR is blocked.

Further, when the manual valve 11 is switched to the "R" position whilethe vehicle is running forwards at a speed above a predetermined speed,the output pressures of both the third solenoid valve 16₃ and the firstsolenoid proportional valve 17₁ are made to be atmospheric pressure. Thefist servo control valve 27 is thus held in the right position, wherebythe hydraulic oil supply to No. 28 oil passage L28, i.e., theestablishment of the reverse transmission train GR, is blocked.

When the manual valve 11 is switched to the "R" position below apredetermined vehicle speed, the output pressure of the first solenoidproportional valve 17₁ is gradually increased to thereby urge the firstservo control valve 27 to the leftward open side. As described above,the hydraulic oil is supplied to the fourth speed hydraulic clutch C4via No. 28 oil passage L28, the servo valve 15 and No. 29 oil passageL29. The first servo control valve 27 is functioned as a pressureregulating valve to thereby control the boosting of the hydraulicpressure in the fourth speed hydraulic clutch C4. Thereafter, themodulator pressure is outputted from the third solenoid valve 16₃ tothereby urge the first servo control valve 27 to the left endmostposition, whereby the hydraulic pressure in the fourth speed hydraulicclutch C4 is maintained at the line pressure. Even if the third solenoidvalve 16₃ fails while it is kept switched on and consequently its outputpressure remains in the atmospheric pressure, the hydraulic pressurerequired to engage the fourth speed hydraulic clutch C4 can be securedby the output pressure of the first solenoid proportional valve 17₁.

When the manual valve 11 is switched from the "R" position to the "D₄ ","D₃ ", "2", or "1" position, the line pressure is inputted from No. 30oil passage L30 which is connected like No. 2 oil passage L2 to No. 1oil passage L1 in each of the above positions, to a second oil chamber15d which is present in an intermediate position of the servo valve 15via the second servo control valve 28 and No. 31 oil passage L31. Theservo valve 15 is thus moved to the left and is switched to the forwardrunning position.

The second servo control valve 28 is urged, by the first speed pressureto be inputted via No. 13 oil passage L13, the output pressure of thesecond solenoid valve 16₂ to be inputted via No. 19 oil passage L19, andthe output pressure of the second pressure regulating valve 14₂ to beinputted via No. 23 oil passage L23, to the left position in which No.30 oil passage L30 and No. 31 oil passage L31 are connected. It is urgedby a spring 28a and the hydraulic pressure in No. 27 oil passage L27 tothe right position in which the connection between No. 30 and No. 31 oilpassages L30, L31 is shut off and No. 31 oil passage L31 is connected toan oil discharge port 28b.

In this manner, in the "R" position, the second servo control valve 28is surely switched to the right position by the line pressure from No.27 oil passage L27. After switching the manual valve 11 to the "D₄ ","D₃ ", "2" or "1" position, the second servo control valve 28 ismaintained in the right position until the first speed pressure rises toa predetermined value. The inputting of the line pressure to the secondoil chamber 15d is thus blocked and the servo valve 15 is retained by anengaging means 15c in the reverse running position. When the first speedpressure has become a predetermined value or above, the second servocontrol valve 28 is switched to the left position, and the line pressureis inputted to the second oil chamber 15d to thereby switch the servovalve 15 to the forward running position. Therefore, even if the manualvalve 11 is switched from the "R" position to the "D₄ ", "D₃ ", "2" or"1" position in a condition in which an accelerator pedal is stepped,the rotation in the reverse direction of the output shaft 7 is beingrestrained, at the time of switching of the servo valve 15, by a torquetransmission in the forward (or positive) direction of rotation via thefirst speed transmission train G1 due to a rise in the first speedpressure. Consequently, the selector gear 8 and a driven gear G4a of thefourth speed transmission train G4 can smoothly be engaged in acondition in which no large relative rotation occurs. Wear of themeshing (or engaging) portions of both the gears 8, G4a can thus beprevented.

In case of an occurrence of an abnormality in that the second servocontrol valve 28 is locked in the right position due to an inclusion ofa foreign matter or the like, or else the servo valve 15 is locked inthe reverse running position even after the servo control valve 28 hasbeen switched to the left position, the selector gear 8 will remain inthe reverse running position even if the manual valve 11 is switchedfrom the "R" position to the "D₄ ", "D₃ ", "2" or "1" position. If thehydraulic oil is consequently supplied to the fourth speed hydraulicclutch C4, the reverse transmission train GR will thus be established.As a solution, in this embodiment, there are provided No. 32 oil passageL32 which is in communication with the left end oil chamber of the thirdshift valve 12₃, and No. 33 oil passage L33 which is connected, in thereverse running position of the servo valve 15, to the second oilchamber 15d of the servo valve 15 via a notched groove 15e. It is thusso arranged that No. 32 oil passage L32 can be connected to No. 30 oilpassage L30 in the right position of the second servo valve 28 and toNo. 33 oil passage L33 in the left position of the second servo valve28, respectively. According to this arrangement, when theabove-described abnormality should occur, the line pressure is inputtedto the left end oil chamber of the third shift valve 12₃ via No. 32 oilpassage L32. Therefore, the third shift valve 12₃ is switched and heldin the right position regardless of the hydraulic pressures in No. 21oil passage L21 and No. 26 oil passage L26 which both urge the thirdshift valve 12₃ leftwards, whereby the hydraulic oil supply to thefourth speed hydraulic clutch C4 is blocked.

Once switched to the left position, the second servo valve 28 is held inthe left position by a self-locking force to be generated by adifference in the pressure-receiving area between right and left landsof an annular groove 28c which connects No. 30 oil passage L30 and No.31 oil passage L31 together. In case, however, the oil level largelyvaries due to a sudden cornering whereby the hydraulic pressure from thehydraulic pressure source 10 instantly stops or disappears, the secondservo control valve 28 may be switched to right position by the force ofthe spring 28a. In such a case, if the second servo control valve 28 isarranged to be urged leftwards only by the first speed pressure, thesecond servo control valve 28 will no longer be returned, at the secondthrough the fourth speeds, to the left position even when the hydraulicpressure restores. As a solution, in this embodiment, the second servocontrol valve 28 is urged to the left position also by the outputpressure of the second pressure regulating valve 14₂ that becomes highat the second and the fourth speeds, as well as by the output pressureof the second solenoid valve 16₂ that becomes high at the third and thefourth speeds. At the first through the third speeds, even if the secondservo control valve 28 does not return to the left position and thethird shift valve 12₃ is switched to the right position by the input ofthe line pressure from No. 32 oil passage L32, the oil supply to, anddischarge from, each of the hydraulic clutches C1 through C4 are notaffected. However, at the fourth speed, the hydraulic oil is supplied tothe second speed hydraulic clutch C2 and, consequently, the speed isdownshifted from the fourth speed to the second speed. Therefore, at thefourth speed, the second servo control valve 28 is urged leftwards bythe output pressure of the second pressure regulating valve 14₂ and theoutput pressure of the second solenoid valve 16₂. Thus, even if one ofthe output pressures does not rise to a normal value after therestoration of the hydraulic pressure, the second servo control valve 28is arranged to be surely switched to the left position.

In the "N" position of the manual valve 11, No. 2 oil passage L2, No. 16oil passage L16, No. 17 oil passage L17, No. 27 oil passage L27, No. 29oil passage L29, and No. 30 oil passage L30 are all opened toatmosphere, and all of the hydraulic clutches C1 through C4 aredisengaged. Further, in the "P" position, No. 27 oil passage L27 isconnected to No. 1 oil passage L1, and the servo valve 15 is switched tothe reverse running position by the inputting of the line pressure viathe first servo control valve 27 and No. 28 oil passage L28. In the "P"position, however, the connection between No. 16 oil passage L16 and No.29 oil passage L29 is shut off to thereby open No. 16 oil passage L16 toatmosphere. There is therefore no possibility that the reversetransmission train GR is established.

The fluid torque converter 2 contains therein a lock-up clutch 2a. Inthe hydraulic oil circuit there is provided a lock-up control portion 29for controlling the operation of the lock-up clutch 2a with thehydraulic oil to be supplied from the regulator 18 via No. 34 oilpassage L34 operating as the working oil.

The lock-up control portion 29 is made up of: a shift valve 30 whichcontrols to switch on and off the lock-up clutch 2a; a changeover valve31 which switches the engaged condition of the lock-up clutch 2a at thetime of being switched on between a locked up condition in which noslipping occurs and a slipping condition; and a pressure regulatingvalve 32 which controls to increase or decrease the engaging force inthe slipping condition.

The shift valve 30 is switchable between the following two positions,i.e.: a right position in which No. 34 oil passage L34 is connected toNo. 35 oil passage L35 which is communicated with a backpressure chamberof the lock-up clutch 2a and in which No. 36 oil passage L36 which iscommunicated with an internal space of the fluid torque converter 2 isconnected, via a throttled portion 30a, to No. 37 oil passage L37 foroil discharge; and a left position in which No. 34 oil passage L34 isconnected to No. 38 oil passage L38 which is communicated with thechangeover valve 31 and also to No. 36 oil passage L36 via the throttledportion 30a, and in which No. 35 oil passage L35 is connected to No. 39oil passage L39 which is communicated with the pressure regulating valve32. The shift valve 30 is controlled by the fourth solenoid valve 16₄.The fourth solenoid valve 16₄ is constituted by a two-way valve whichopens to atmosphere No. 40 oil passage L40 which is connected to No. 24oil passage L24 on the output side of the modulator valve 19 via athrottle 16₄ a. The shift valve 30 is urged to the left position by thehydraulic pressure in No. 24 oil passage L24, i.e., by the modulatorpressure, and is urged to the right position by a spring 30b and thehydraulic pressure in No. 40 oil passage L40. When the fourth solenoidvalve 16₄ is closed and the hydraulic pressure in No. 40 oil passage L40is boosted to the modulator pressure, the shift valve 30 is switched tothe right position. When the fourth solenoid valve 16₄ is opened and thehydraulic pressure in No. 40 oil passage L40 is lowered to theatmospheric pressure, the shift valve 30 is switched to the leftposition.

The changeover valve 31 is switchable between the following twopositions, i.e., a right position in which No. 41 oil passage L41 whichis communicated with the internal space of the fluid torque converter 2is connected to No. 42 oil passage L42 which is communicated with a leftend oil chamber of the pressure regulator valve 32, and a left positionin which No. 42 oil passage L42 is opened to atmosphere and in which No.38 oil passage L38 is connected to No. 36 oil passage L36. Thechangeover valve 31 is urged to the right position by a spring 31a andis urged to the left position by the hydraulic pressure in No. 43 oilpassage L43 which is connected to the right-end oil chamber.

The pressure regulating valve 32 is switchable between the following twopositions, i.e., a right position in which No. 39 oil passage L39 isconnected to No. 34 oil passage L34 and in which No. 41 oil passage L41is connected to No. 37 oil passage L37 via a throttle 32a, and a leftposition in which the connection between No. 39 oil passage L39 and No.34 oil passage L34 is shut off and connect No. 39 oil passage L39 to athrottled oil discharge port 32b, and in which the connection betweenNo. 41 oil passage L41 and No. 37 oil passage L37 is shut off. Thepressure regulating valve 32 is urged rightwards by a spring 32c and thehydraulic pressure in No. 42 oil passage L42, and is urged leftwards bythe hydraulic pressure in No. 39 oil passage L39 and the hydraulicpressure in No. 43 oil passage L43. Here, let the pressure receivingarea to receive the hydraulic pressure in No. 39 oil passage L39 and thepressure receiving area to receive the hydraulic pressure in No. 42 oilpassage L42 be both s1, the pressure receiving area to receive thehydraulic pressure in No. 43 oil passage L43 be s2, the hydraulicpressures in No. 39 oil passage L39, No. 42 oil passage L42 and No. 43oil passage L43 be Pa, Pb and Pc, respectively, and the urging force ofthe spring 32c be F. Then, we have

    s1·Pb+F=s1·Pa+s2·Pc

    Pb-Pa=(s2·Pc-F)/s1

The differential pressure between the hydraulic pressure in No. 42 oilpassage L42 and the hydraulic pressure in No. 39 oil passage L39 isincreased or decreased depending on the hydraulic pressure in No. 43 oilpassage L43.

No. 43 oil passage L43 is connected, in the right position of thechangeover valve 13, to No. 25 oil passage L25 on the output side of thefirst solenoid proportional valve 17₁ and, in the left position of thechangeover valve 13, to No. 26 oil passage L26 on the output side of thesecond solenoid proportional valve 17₂. In this manner, the changeovervalve 31 and the pressure regulating valve 32 are controlled by thefirst solenoid proportional valve 17₁ at the time of the first and thethird speeds in which the changeover valve 13 is in the right position,and by the second solenoid proportional valve 17₂ at the time of thesecond and the fourth speeds in which the changeover valve 13 is in theleft position.

When the shift valve 30 is in the right position, the working oil fromNo. 34 oil passage L34 is supplied to the back pressure chamber of thelock-up clutch 2a via the shift valve 30 and No. 35 oil passage L35.Also, the internal space of the fluid toque converter 2 is connected toNo. 37 oil passage L37 via No. 41 oil passage L41 and the pressureregulating valve 32 as well as via No. 36 oil passage L36 and thethrottled portion 30a of the shift valve 30. Due to the oil dischargefrom the internal space via No. 37 oil passage L37, the internalpressure in the internal space is lowered, whereby the lock-up clutch 2abecomes a condition of being switched off, i.e., in a condition in whichthe engagement is released.

When the shift valve 30 is switched to the left position, the backpressure chamber of the lock-up clutch 2a is connected to No. 39 oilpassage L39 via No. 35 oil passage L35 and the shift valve 30. While thechangeover valve 31 is in the right position, the internal space of thefluid torque converter 2 is connected to No. 34 oil passage L34 via No.36 oil passage L36 and the throttled portion 30a of the shift valve 30,as well as to No. 42 oil passage L42 via No. 41 oil passage L41 and thechangeover valve 31. The differential pressure between the internalpressure in the internal space and the internal pressure in the backpressure chamber can be controlled for increase or decrease by thathydraulic pressure in No. 43 oil passage L43 which is inputted to thepressure regulating valve 32. In this manner, the lock-up clutch 2a isengaged, in a slipping condition, with an engaging force correspondingto the output pressure of the first solenoid proportional valve 17₁ orthe second solenoid proportional valve 17₂.

When the hydraulic pressure in No. 43 oil passage L43 has become apredetermined value and above whereby the changeover valve 31 isswitched to the left position, No. 42 oil passage L42 is opened toatmosphere and consequently the pressure regulating valve 32 is switchedto, and retained in, the left position. The back pressure chamber of thelock-up clutch 2a thus remains connected to the oil discharge port 32bof the pressure regulating valve 32 via No. 35 oil passage L35, theshift valve 30, and No. 39 oil passage L39. O n the other hand, thehydraulic oil is supplied from No. 34 oil passage L34 to the internalspace of the fluid torque converter 2 via the shift valve 30, No. 38 oilpassage L38, the changeover valve 31, and No. 36 oil passage L36.Further, since the connection between No. 41 oil passage L41 and No. 37oil passage L37 is shut off by the switching of the pressure regulatingvalve 32 to the left position, the internal pressure inside the internalspace is maintained at a relatively high pressure that is set by a checkvalve 33 which is connected to No. 41 oil passage L41. The lock-upclutch 2a is thus engaged in the locked up condition.

In the figure, numeral 34 denotes an oil cooler interposed in No. 37 oilpassage L37, numeral 35 denotes a check valve for the oil cooler,numeral 36 denotes a throttle member which is interposed in alubricating oil passage LB which supplies leaked oil from the regulator18 to lubricated portions in each of the shafts 3, 5, 7 of thetransmission.

Explanation will now be made about the control of the first and thesecond solenoid proportional valves 17₁, 17₂ at the time of speedchanging. In the following explanations, the following definitions areused. Namely, the output pressure of the solenoid proportional valvewhich controls the hydraulic pressure of the hydraulic clutch on theengaging side to be engaged at the time of speed changing is defined tobe an ON pressure. The output pressure of the solenoid proportionalvalve which controls the hydraulic pressure of the hydraulic clutch onthe disengaging side to be disengaged or released at the time of speedchanging is defined to be an OFF pressure.

The speed change control is largely classed into an upshifting control,a downshifting control, and an in-gear control (i.e., a control ofgear-in or of gear engagement) at the beginning of switching from the"P" or "N" range (position) to the "D₄ ", "D₃ ", "2", "1" or "R" range.These controls are performed in the following manner by using thefollowing values: i.e., proportional valve monitor values MAT whichrepresent, as shown in FIG. 5A, the relationship in magnitude (high orlow) of the output pressures of the first solenoid proportional valve17₁ and the second solenoid proportional valve 17₂, and the controlmodes during the in-gear control; upshifting monitor values MUP whichrepresent, as shown in FIG. 5B, the control modes of the ON pressure andthe control modes of the OFF pressure at the time of upshifting; anddownshifting monitor values MDN which represent, as shown in FIG. 5C,the control modes of the ON pressure and the control modes of the OFFpressure at the time of downshifting.

The upshifting control is performed in the procedures shown in FIG. 7.Details of this upshifting control will now be explained with referenceto FIG. 6 which schematically shows the changes in the ON pressure, theOFF pressure, and the input and output speed ratio "Gratio" (Nout/Nin)of the transmission, respectively, at the time of upshifting. The"Gratio" may vary or fluctuate slightly depending on the pulsations inthe speed detecting pulses, noises, or the like. However, when ahydraulic clutch has completely been engaged, "Gratio" will fall withina range between a predetermined upper limit value YG(N)H and a lowerlimit value YG(N)L which are based on a gear ratio of each speed stage.

The upshifting control is started when a speed stage designation signalSH which designates a speed stage to be established is switched to asignal which designates a higher speed stage G(N+1) than the speed stageG(N) that is now being established. In the upshifting control, MAT isfirst set to "A, B" in step S1. Once MAT has thus been set, the firstand the second shift valves 12₁, 12₂ are switched to a condition inwhich the upshifting can be made. Then, in step 2, a discrimination ismade whether the value (MUP(ON)) on the side of ON of MUP is "0" or not.MUP is initially set to "0,0" and, after making a judgement of "YES" instep S2, the program (or process) proceeds to step S3. In step S3, theremaining time TM of a subtractive timer (subtraction type of timer)built in the electronic control circuit 20 is set to a predeterminedinitial value TMST. Also, in step S4, initial setting is made of variouskinds of values to be used in the operation (or computation) of the ONpressure and the OFF pressure. Then, in step S5, a setting of MUP(ON)=1is made. Further, in step S6, a standard (or reference) value QUPONA ofthe ON pressure in a response pressure mode is computed (S6). Theresponse pressure mode is a control mode in which a play of a piston ina hydraulic clutch on the engaging side is removed to thereby perform asubsequent clutch pressure increase with a good response. The valueQUPONA is set to an appropriate value according to the vehicle speed andthe throttle opening, and decreases with the lapse of time.

Then, the program proceeds to step S7, in which a check is made of avalue of a flag FTIP which is set to "1" at the time of manual speedchanging, i.e., at the time of speed changing by switching the ranges,or at the time of speed changing by lever operation in a transmission inwhich a step-wise speed changing (i.e., one speed stage at a time) by alever operation is enabled. If FTIP=0, the program proceeds to step S8,in which the processing is performed of setting QUPON which is a commandvalue of the ON pressure to QUPONA. If FTIP=1, the program proceeds tostep S9, in which a processing is performed of setting QUPON to a valuewhich is obtained by adding a predetermined boosting correction valueQUPONX to QUPONA (S9). After the processing in steps S8 and S9, theprogram proceeds to step S10, in which a processing is performed ofcomputing a command value QUPOFF of the OFF pressure, which is describedin detail hereinafter. Then, the program proceeds to step S11, in whichthe following processing of selecting the proportional valves isperformed. Namely, a command value of the output pressure of thatsolenoid proportional valve, between the first and the second solenoidproportional valves 17₁, 17₂, which controls the hydraulic pressure ofthe hydraulic clutch on the engaging side in the speed changing at thistime is made to be QUPON, and a command value of the output pressure ofthe solenoid proportional valve which controls the hydraulic pressure ofthe hydraulic clutch on the disengaging side is made to be QUPOFF. Thefirst upshifting control processing is thus completed.

In the next upshifting control processing, since the setting ofMUP(ON)=1 has already been made in step S5 last time, a judgement of"NO" is made in step S2. At this time, the program proceeds to step S12and a discrimination is made whether or not the time of lapse from thestart of the upshifting (TMST-TM) has reached a predetermined timeYTMUP1. The time YTMUP1 is set longer than an ordinary time required forupshifting. When TMST-TM>YTMUP1, a judgement is made that an upshiftingcontrol has failed, and the program proceeds to step S13. in step S13, aprocessing to complete the upshifting in which MAT is set to "A,0" (atthe time of upshifting from the second speed to the third speed), or to"0, B" (at the time of upshifting other than from the second speed tothe third speed), and MUP is set to "0,0", and also TM is reset to zerois performed. When MAT is set to "A,0" or "0,B" in this processing, thechangeover valve 13 is switched to a position which is different fromthe present position, whereby the hydraulic pressure in the hydraulicclutch on the engaging side becomes the line pressure and the hydraulicpressure of the hydraulic clutch on the disengaging side becomesatmospheric pressure.

If TMST-TM<YTMUP1, the program proceeds to step S14 to judge whether thepreparation for engagement of the hydraulic clutch on the engaging side(ON clutch) has been made or not. Details of this processing are shownin FIG. 8. First, a discrimination is made in step S14-1 whether or notMUP is "1,1" or "1,2". If the result of the discrimination is "YES", theprogram proceeds to step S14-2. In step S14-2, a discrimination is madewhether "Gratio" has fallen below that lower limit value YG(N)L forjudging the clutch engagement which is set based on the gear ratio ofthe speed stage established before speed changing. If "Gratio"<YG(N)L,the program proceeds to step S14-3, in which a flag FCOFFS to be resetto "0" in the above-described step S4 is set to "1". Then, in stepS14-4, a discrimination is made whether MUP is "2,2" or not. If theresult of this discrimination is "YES", the program proceeds to stepS14-5 to discriminate whether FCOFFS=1 or not. If FCOFFS=1, adiscrimination is made in step S14-6 whether the throttle opening θexceeds a predetermined value YθCONOK or not. If θ>YθCONOK, the programproceeds to step S14-7, in which a discrimination is made whether"Gratio" exceeds a predetermined value YGCONOK which is set a littlelarger than YG(N)L. If "Gratio">YGCONOK, the program proceeds to stepS14-8, in which a flag FCONOK to be reset to "0" in step S4 is set to"1". In case θ≦YθCONOK or "Gratio"≦YGCONOK, the program proceeds to stepS14-9, in which FCONOK is reset to "0".

It is when slipping has occurred in the hydraulic clutch on thedisengaging side by the control of the OFF pressure in a subtractionmode, which is described hereinafter, that the condition of"Gratio"<YG(N)L is satisfied when MUP is "1,1" or "1,2". Further, it iswhen the hydraulic clutch on the engaging side has begun to secure anengaging force, i.e., when the preparation for engaging the hydraulicclutch on the engaging side has been completed by the control of the ONpressure in an addition mode, which is described hereinafter, that thecondition of "Gratio">YGCONOK is satisfied when MUP is "2,2". If thecondition of "Gratio"<YG(N)L is not satisfied when MUP is "1,1" or"1,2", then FCOFFS is not set to "1". In this case, even if thecondition of "Gratio">YGCONOK has been satisfied when MUP is "2,2",FCONOK remains to be zero (FCONOK=0).

The degree of change in the engine output torque with the degree ofthrottle opening becomes large in a small throttle opening region. Whenthe throttle opening becomes small, the output torque largely decreases.As a consequence, the slipping of the hydraulic clutch on thedisengaging side decreases to thereby sometimes satisfy the condition of"Gratio">YGCONOK. Therefore, in the small throttle opening region inwhich θ≦YθCONOK, FCONOK is made to be zero (FCONOK=0), and the settingof FCONOK based on "Gratio" is made only in the medium/large throttleopening region in which the output torque does not largely vary. Thesetting of FCONOK=1 is thus prevented when the preparation forengagement of the hydraulic clutch on the engaging side has not beenmade yet.

After having made the processing of judging whether the preparation forengagement of the hydraulic clutch on the engaging side has been made ornot as described above, a discrimination is made in step S15 whetherMUP(ON)=1 or not. Since in the second upshifting control processing,MUP(ON) has already been set to 1 (MUP(ON)=1), a judgement of "YES" ismade in step S15. The program proceeds to step S16, in which adiscrimination is made whether the time of lapse from the start ofupshifting (TMST-TM) has reached a predetermined time YTMUP2 or not. IfTMST-TM <YTMUP2, the program proceeds to S5 and following steps (i.e.,steps that follow). When TMST-TM ≧TMUP2, the program proceeds to stepS17, in which the value of MUP on the ON side is set to "2". Then,ΔQUPONA is set to a relatively small value in step S18' and the programproceeds to step S18, in which an adding processing is performed to makeQUPONA to a value which is obtained by adding ΔQUPONA to the precedingvalue of QUPONA. The program then proceeds to step S7 and followingsteps. In this manner, a control in the addition mode to increasestepwise the ON pressure is started.

When a setting of MUP(ON)=2 is made in step S17, a determination of "NO"is made in step S15 in the next upshifting control processing. Theprogram thus proceeds to step S19, in which a discrimination is madewhether MUP(ON)=2 or not. Here, a discrimination of "YES" is made andthe program proceeds to step S20, in which a discrimination is madewhether "Gratio" has exceeded that upper limit value YG(N)H for judgingthe engagement of the hydraulic clutch which is set based on the gearratio of the speed stage established before speed changing. Then, if"Gratio"<YG(N)H, the program proceeds to step S21 to discriminatewhether FCONOK=1 or not. If FCONOK=0, the program proceeds to step S17and following steps to continue the control in the addition mode.

If FCONOK=1, the value of TM at that time is stored in step S22 asTMSTA. Then, after setting MUP to "3,3" in step S23, the programproceeds to step S25 and following steps. In the next upshifting controlprocessing, a determination of "NO" is made in step S19. The programthus proceeds to step S24, in which a discrimination is made whetherMUP(ON)=3 or not, and a discrimination of "YES" is made therein. At thistime, YTMUP3 is set in step S25, and the program then proceeds to stepS26, in which a discrimination is made whether the time of lapse fromthe time when CONOK=1 has been attained, i.e., from the time when thepreparation for engagement of the hydraulic clutch on the engaging sidehas been completed (TMSTA-TM) has reached YTMUP3 or not. The valueYTMUP3 is set to a table value which has the vehicle speed V as aparameter, such that YTMUP3 becomes longer with the increase in thevehicle speed. While TMSTA-TM<YTMUP3, ΔQUPONA is set to a relativelylarge value in step S18", and the program proceeds to step S18 andfollowing steps. The control in the addition mode is thus continued.

When TMSTA-TM≧YTMUP3, the program proceeds to step S27, in which adiscrimination is made whether FTIP=1 or not. If FTIP=0, the programproceeds to step S28, in which a reference value QUPONB of the ONpressure in a bottom up mode is set to a value which is obtained byadding to the final value of QUPONA a value QUPONBO to be obtaineddepending on the vehicle speed and the throttle opening. If FTIP=1, theprogram proceeds to step S29, in which QUPONB is set to a value which isobtained by further adding to the above-described value a predeterminedboosting correction value QUPONY. The value QUPONY is set to a valuewhich is smaller than the boosting correction value QUPONX to be addedin step S9. When the processing of setting QUPONB in step S28 or S29 iscompleted, the program proceeds to step S30, in which a setting ofMUP(ON)=4 is made. Then, in step S31, QUPON is set to QUPONB, therebystarting the control of the ON pressure in the bottom up mode. When adiscrimination of "Gratio">YG(N)H is made in step S20, MUP is set to"3,3" in step S32 and the program proceeds directly to step S27.

In the next upshifting control processing, since the setting ofMUP(ON)=4 has already been made in step S30 last time, a judgement of"NO" is made in step S24. The program thus proceeds to step S33 fordiscriminating whether MUP(ON)=4 or not, and a judgement of "YES" ismade therein. At this time, the program proceeds to step S34, in which adiscrimination is made whether the time of lapse from the start ofupshifting (TMST-TM) has reached a predetermined time YTMUP4. WhileTMST-TM<YTMUP4, the program proceeds to step S27 a nd following stepsand the control in the bottom up mode is continued. When TMST-TM aYTMUP4, a discrimination is made in step s35 whether "Gratio" hasexceeded a predetermined value YGUPT or not. While "Gratio"<YGUPT, theprogram proceeds to step S27 and following steps to continue the controlin the bottom up mode.

When "Gratio"≧YGUPT, the program proceeds to step S36 to set MUP to"5,5" and then proceeds to step S37, in which the value of TM at thattime is stored as TMSTB. Then, the program proceeds to step S38, inwhich QUPON is set to a value which is obtained by adding QUPONC to thefinal value of QUPONB. Since the value of QUPONC has already been resetto zero in step S4, QUPON becomes equal to QUPONB (QUPON=QUPONB), andthe control in the bottom up mode is continued.

In the next upshifting control processing, since MUP h a s already beenset to "5,5" in step S36 last time, a judgement of "NO" is made in stepS33, and the program proceeds to step S39 for discriminating whetherMUP(ON)=5 or not, and a judgement of "YES" is made therein. At thistime, a discrimination is made in step S40 whether the time of lapsefrom the start of upshifting (TMST-TM) has reached a predetermined timeYTMUP5. If TMST-TM≧YTMUP5, the program proceeds to step S41, in which adiscrimination is made whether "Gratio" is above that lower limit valueYG(N+1)L for judging the clutch engagement which is set based on thegear ratio of the speed stage established after speed changing. IfTMST-TM<YTMUP5 or "Gratio"<YG(N+1), the program proceeds to step S36 andfollowing steps, and the control in the bottom up mode is continued.

When "Gratio"≧YG(N+1)L, MUP is set to "7,7" in step S42 and the programthen proceeds to step S43, in which QUPONC is set to a value which isobtained by adding a predetermined value ΔQUPONC to the previous valueof QUPONC. Then, in step S44, a discrimination is made whether "Gratio"lies within a range between those lower limit value YG(N+1)L and upperlimit value YG(N+1)H for judging the clutch engagement which are setbased on the gear ratio of the speed stage established after speedchanging. If the result of this discrimination is "NO", the programproceeds to step S37 and following steps. In this case, since QUPONCincreases by ΔQUPONC in the operation (or computation) in step S43,QUPON to be obtained in step S38 also gradually increases, and thecontrol of the ON pressure in an end mode is started.

In the next upshifting control processing, since MUP has already beenset to "7,7" in step S42 last time, a judgement of "NO" is made in step539, and the program proceeds to step S42 and following steps. In thiscase, if YG(N+1)L≦"Gratio"≦YG(N+1)H, i.e., if the clutch on the engagingside has completed engagement, the program proceeds to step S45. In stepS45, a discrimination is made whether the time of duration of engagementcompletion (TMSTB-TM) has reached a predetermined time YTMUP6. WhileTMSTB-TM<YTMUP6, the program proceeds to step S38 and the control in theend mode is continued. When TMSTB-TM≧YTMUP6, the program proceeds tostep S13, in which a processing of upshifting completion is performed.

Details of operational processing of QUPOFF in step S10 are shown inFIG. 9. First, in step S10-1, the value QUPOFFB of the OFF pressure in abottom down mode is set to an appropriate value depending on thethrottle opening. Then, in step S10-2, a discrimination is made whetherthe value of MUP on the OFF side (MUP(OFF)) is "0" or not. SinceMUP(OFF) has already been set to zero (MUP(OFF)=0) in the upshiftingcontrol processing in the first time, a judgement of "YES" is made instep S10-2. The program thus proceeds to step S10-3, in which a settingof MUP(OFF)=1 is made. Then, the program proceeds to step S10-4, inwhich a standard (reference) value QUPOFFA of the OFF pressure in aninitial pressure mode is set to an appropriate value depending on thethrottle opening and the speed ratio of the fluid torque converter 2.Further, in step S10-5, a processing of operating (computing) a value ofthe OFF pressure in the subtraction mode is performed. Details of thisprocessing are shown in FIG. 10. First, in step S10-5-1, adiscrimination is made whether MUP(OFF)=1 or not. If MUP(OFF)=1, both asubtraction value ΔQUPOFF and a feedback correction value QWP are resetto zero in step S10-5-2. If MUP(OFF)≠1, ΔQUPOFF is set to apredetermined value in step S10-5-3 and, also, QWP is computed by afunctional operation from a deviation between "Gratio" at the presenttime and that target value of clutch slipping YG(N)S which is set alittle lower than the lower limit value YG(N)L for judging the clutchengagement, the lower limit value being set based on the gear ratio ofthe speed stage established before speed changing. Then, in stepS10-5-4, there is performed a processing to make QUPOFFA to a valuewhich is obtained by subtracting ΔQUPOFF-QWP from the value of QUPOFFAthat is set in step S10-4. Finally, by the processing in steps S10-5-5and S10-5-6, QUPOFFA is made so as not fall below QUPOFFB.

After the processing in step S10-5 has been completed as describedabove, in step S10-6, a processing is made of making QUPOFF to QUPOFFA.An operational processing of QUPOFF in the first time of upshiftingcontrol processing is thus completed. In the second time of upshiftingcontrol processing, since the setting of MUP(OFF)=1 has already beenmade in step S10-3 last time, a judgement of "NO" is made in step S10-2.The program thus proceeds to step S10-7 for making a discrimination asto whether MUP(OFF)=1 or not, and a judgement of "YES" is made therein.At this time, the program proceeds to step S10-8, in which adiscrimination is made whether the time of lapse from the start ofupshifting (TMST-TM) has reached a predetermined time YTMUP7. IfTMST-TM<YTMUP7, the program proceeds to step S10-3 and following steps.In this case, QUPOFF becomes equal to the value of QUPOFFA which isobtained in step S10-4, and the control in the initial pressure mode isperformed.

When TMST-TM≧YTMUP7, a setting of MUP(OFF)=2 is made in step S10-9 andthen the program proceeds to step S10-4. In this case, QUPOFF becomes avalue which is obtained in step S10-4 by subtracting ΔQUPOFF-QWP fromQUPOFFA, and a control in the subtraction mode is started. In the nextprocessing of upshifting control, since the setting of MUP(OFF)=2 hasalready been made in step S10-9 last time, a judgement of "NO" is madein step S10-7. The program thus proceeds to step S10-10 for making adiscrimination as to whether MUP(OFF)=2 or not. A judgement of "YES" ismade therein and the program proceeds to step S10-9 and following steps,and the control in the subtraction mode is continued. In the subtractionmode, QUPOFF sequentially decreases, and the hydraulic clutch on thedisengaging side begins to slide, with the result that "Gratio" fallsbelow YG(N)L. When "Gratio"<YG(N)S, a condition of QWP>0 is attained andthe subtraction range of QUPOFFA becomes smaller. A feedback control isthus made so as to attain a condition of "Gratio"=YG(N)S.

When MUP is set to "3,3" in the above-described step S23 or S32, adiscrimination of "NO" is made in step S10-10. The program thus proceedsto step S10-11 for making a discrimination as to whether MUP(OFF)=3 ornot, and a judgement of "YES" is made therein. At this time, aftersetting YTMUP8 in step S10-12, the program proceeds to step S10-13, inwhich a discrimination is made whether the time of lapse from the timeof completion of preparation for engagement of the hydraulic clutch onthe engaging side (TMSTA-TM) has reached YTMUP8. The value YTMUP8 is setto a table value with the vehicle speed V as a parameter so that itbecomes shorter with the increase in the vehicle speed. WhileTMSTA-TM<YTMUP8, the program proceeds to step S10-4 and following stepsand the control in the subtraction mode is continued. WhenTMSTA-TM≧YTMUP8, a setting of MUP(OFF)=4 is made in step S10-14, and theprogram then proceeds to step S10-15. In step S10-15, QUPOFF is set toQUPOFFB, and the control in the bottom down mode is started. In the nextprocessing of upshifting control, since the setting of MUP(OFF)=4 hasalready been made last time in step S10-14, a judgement of "NO" is madein step S10-11. The program thus proceeds to step S10-16 for making adiscrimination as to whether MUP(OFF)=4 or not. A judgement of "YES" ismade therein and the program proceeds to step S10-14 and followingsteps, and a control in the bottom down mode is continued.

When MUP is set to "5,5" in the above-described step S36, a judgement of"NO" is made in step S10-16. The program thus proceeds to step S10-17for making a discrimination as to whether MUP(OFF)=5 or not, and ajudgement of "YES" is made therein. At this time, the program proceedsto step S10-18, and QUPOFF is set to a value QUPOFFC which graduallydecreases from QUPOFFB depending on "Gratio". A control in a tail modeis thus performed. Then, when MUP has been set to "7,7" in theabove-described step S42, a judgement of "NO" is made in step S10-17.The program thus proceeds to step S10-19, and a control is performed inthe end mode in which QUPOFF is made to zero.

In the above-described upshifting control, by the control of the OFFpressure in the subtraction mode, the OFF pressure isfeedback-controlled so that "Gratio" becomes YG(N)S. A slight slippingthus occurs in the hydraulic clutch on the disengaging side. Since thecontrol of the ON pressure in the addition mode is performed in thiscondition, "Gratio" sensitively varies with the engaging force of thehydraulic clutch on the engaging side. Therefore, the point of time ofcompletion of preparation for engagement of the hydraulic clutch on theengaging side can be detected by the increase in "Gratio" to YGCONOK.Conventionally, the following arrangement is also known. Namely, inorder to prevent the engine from racing, the ON pressure is graduallyincreased while controlling the OFF pressure such that the hydraulicclutch on the disengaging side does not slip, i.e., such that the"Gratio" lies within a range between YG(N)L and YG(N(H). When "Gratio"has exceeded YG(N)H as a result of decrease in the rotational speed ofthe input shaft due to simultaneous engagement of the hydraulic clutchon the disengaging side and the hydraulic clutch on the engaging side, ajudgement is made that the speed change condition has transferred to aninertia phase. The OFF pressure is then rapidly decreased and, further,the ON pressure is rapidly increased. However, if the rate of gradualincrease in the ON pressure is made large, the engaging force of thehydraulic clutch on the engaging side at the time of transferring to theinertia phase becomes excessive, resulting in the occurrence of shocks.Therefore, the rate of gradual increase in the ON pressure cannot bemade so large and, consequently, it takes much time for the speed changecondition to transfer to the inertia phase. This results in a longertime required in the speed changing. On the other hand, in the presentembodiment, the completion of preparation for engagement of thehydraulic clutch on the engaging side is detected as described above,and the OFF pressure is rapidly decreased by switching to the bottomdown mode at a lapse of YTMUP8 from the point of time of completion ofpreparation for engagement. Therefore, the speed change condition can betransferred at an early time to the inertia phase (a condition of"Gratio">YG(N)H) while preventing the engine from racing, therebyenabling to reduce the time required for speed changing. Further, in thepresent embodiment, since the rate of gradual increase in the ONpressure in the addition mode is increased from the point of time ofcompletion of preparation for engagement, the transferring to theinertia phase can still further be accelerated.

When the vehicle speed becomes high, a delay occurs in the decrease ordrop in the hydraulic pressure in the hydraulic clutch on thedisengaging side under the influence of centrifugal force. In thepresent embodiment, however, since YTMUP8 is set so as to become shorterwith the increase in the vehicle speed, the timing of switching of theOFF pressure to the bottom down mode is accelerated at a high vehiclespeed. Therefore, the occurrence of shocks is prevented as a result ofincrease in simultaneous engagement due to a delay in the pressuredecrease in the hydraulic clutch on the disengaging side at a highvehicle speed. Further, in the present embodiment, in order toaccelerate the speed changing after having transferred to the inertiaphase, the ON pressure is rapidly increased by the switching to thebottom up mode at a lapse of YTMUP3 from the point of time of completionof preparation for engagement of the hydraulic clutch on the engagingside. However, since YTMUP3 is set so as to become longer with theincrease in the vehicle speed, the occurrence of shocks due to anincrease in simultaneous engagement at a high vehicle speed can surelybe prevented.

If the control of the OFF pressure in the subtraction mode has failed, acondition of "Gratio">YG(N)H sometimes occurs by the simultaneousengagement due to an increase in the ON pressure while giving rise toslipping in the hydraulic clutch on the disengaging side. In such acase, by judging that the speed change condition has transferred to theinertia phase, the control mode of the OFF pressure and the control modeof the ON pressure are immediately switched to the bottom down mode andthe bottom up mode, respectively.

At the time of manual speed changing in which a condition of FTIP=1 issatisfied, it is desired to shorten the speed change time below that atthe time of automatic speed changing. For that purpose, in the presentembodiment, the ON pressure is corrected by boosting at the time ofmanual speed changing, thereby shortening the speed change time.Further, in the present embodiment, the boosting correction value QUPONXin the response pressure mode and the addition mode before thetransferring to the inertia phase is set to a relatively large value,thereby shortening the time to the transferring to the inertia phase.Further, the boosting correction value QUPONY in the bottom up modeafter transferring to the inertia phase is set to a relatively smallvalue, thereby preventing the shocks from becoming large.

The downshifting control is performed in the procedures shown in FIG.12. Details thereof ar e explained with reference to FIG. 11 whichschematically shows the changes in the ON pressure, the OFF pressure,and the "Gratio", respectively, at the time of downshifting.

The downshifting control is started when the speed stage designationsignal SH is switched to a signal which designates a lower speed stageG(N-1) than the speed stage G(N) that is now being established. In thedownshifting control, MAT is first set to "A,B" in step S101. When MAThas thus been set, the changeover valve 13 is switched to a positionwhich is different from the present position. Then, a discrimination ismade in step S102 whether the value of MDN on the ON side (MDN(ON)) is"0" or not. Since MDN is initially set to "0,0", a judgement of "YES" ismade in step S102. The program thus proceeds to step S103, in which TMis set to TMST. Further, in step S104, initial setting is made ofvarious values to be used in the operation (or computation) of the ONpressure and the OFF pressure. Then, after passing through a step ofS104' which is described hereinafter, the program proceeds to step S105,in which a setting of MDN(ON)=1 is made. Further, in step S106, a valueQDNONA of the ON pressure in the response pressure mode is set to anappropriate value depending on the vehicle speed and the throttleopening. The value QDNONA decreases with the lapse of time. Then, instep S107, a command value QDNON of the ON pressure is set to QDNONA,and an operational processing of the command value QDNOFF of the OFFpressure to be described hereinafter is performed in step S108.Thereafter, the program proceeds to step S109, in which the selectionprocessing of proportional valves is performed in the following manner.Namely, between the solenoid proportional valves 17₁, 17₂, a commandvalue of the output pressure of the solenoid proportional valve whichcontrols the hydraulic pressure of a hydraulic clutch on the engagingside in the speed change at this time is made to be QDNON, and a commandvalue of the output pressure of the solenoid proportional valve whichcontrols the hydraulic pressure of a hydraulic clutch on the disengagingside is made to be QDNOFF. The downshifting control processing of thefirst time is thus completed.

In the next downshifting control processing, since the setting ofMDN(ON)=1 has already been made in step S105 last time, a judgement of"NO" is made in step S102. At this time, the program proceeds to stepS110, in which a discrimination is made whether the time of lapse fromthe start of downshifting (TMST-TM) has reached a predetermined timeYTMDN1. The value YTMDN1 is set to a value which is slightly longer thanan ordinary time required for downshifting. When TMST-TM≧YTMDN1, ajudgement is made that the downshifting control has failed, and theprogram thus proceeds to step S111. In this step, there is performed adownshifting completion processing in which MAT is set to "0,B" (at thetime of downshifting from the third speed to the second speed) or to"A,0" (at the time of downshifting other than from the third speed tothe second speed). Further, MDN is reset to "0,0", and TM is reset tozero. When MAT is set to "0,B" or "A,0" in this processing, thepositions of the first and the second shift valves 12₁, 12₂ are switchedto the condition of performing the downshifting. The hydraulic pressurein the hydraulic clutch on the engaging side becomes the line pressure,and the hydraulic pressure in the hydraulic clutch on the disengagingside becomes atmospheric.

If TMST-TM<YTMDN1, the program proceeds to step S112 and adiscrimination is made whether MDN(ON)=1 or not. In the seconddownshifting control processing, since MDN(ON)=1, a judgement of "YES"is made in step S112. The program thus proceeds to step S113, in which adiscrimination is made whether "Gratio" has exceeded a predeterminedvalue YGDNS or not. If "Gratio">YGDNS, the program proceeds to stepS114, in which a discrimination is made whether the time of lapse fromthe start of downshifting (TMST-TM) has reached a predetermined timeYTMDN2. If TMST-TM<YTMDN2, the program proceeds to step S105 andfollowing steps to thereby perform the control of the ON pressure in theresponse pressure mode.

When "Gratio"≦YGDNS or TMST-TM≧YTMDN2, the program proceeds to stepS115, in which a setting of MDN(ON)=2 is made, and then proceeds to stepS116, in which the value QDNONB of the ON pressure in a low pressurecorrection mode is set to an appropriate value depending on the vehiclespeed and the throttle opening. In step S117, there is performed anannealing processing in which QDNONB is gradually changed from QDNONA toa value to be set as above. Then, in step S118, QDNON is set to QDNONBto thereby start the control of the ON pressure in the low pressurecorrection mode.

In the next downshifting control processing, since the setting ofMDN(ON)=2 has already been made in step S115 last time, a judgement of"NO" is made in step S112. The program thus proceeds to step S119 formaking a discrimination as to whether MDN(ON)=2 or not, and a judgementof "YES" is made therein. At this time, the program proceeds to stepS120 and a discrimination is made whether "Gratio" has exceeded YGDNS ornot. If "Gratio">YGDNS, the program proceeds to step S121, and adiscrimination is made whether the time of lapse from the start ofdownshifting (TMST-TM) has reached a predetermined value YTMDN3. IfTMST-TM<YTMDN3, the program proceeds to step S115 and following steps tocontinue the control in the low pressure correction mode.

Once "Gratio"≦YGDNS, MDN is set to "3,3" in step S122 and the programthen proceeds to step S123. If the condition of TMST-TM≧YTMDN3 issatisfied while "Gratio">YGDNS, the program proceeds directly to stepS123, in which a setting of MDN(ON)=3 is made. Then, in step S124, astandard (reference) value QDNONC of the ON pressure in a synchronousmode is set to an appropriate value depending on the vehicle speed andthe throttle opening. In step S125, an annealing processing to graduallychange QDNONC from QDNONB to the above-described value is performed.Then, the program proceeds to step S126, in which a check is made of avalue of a flag FTBD which is set to "1" when the speed stagedesignating signal SH is switched, during the downshifting control, to asignal specifying a speed stage G(N-2) of further lower speed. Then, ifFTBD=0, the program proceeds to step S127, in which QDNON is set to avalue which is obtained by adding QDNOND to QDNONC. The value QDNOND isset to zero in the initial setting and, therefore, the condition becomesQDNON=QDNONC. The control of the ON pressure in the synchronous mode isthus started.

In the next downshifting control processing, since the setting ofMDN(ON)=3 has already been made in step S123 last time, a judgement of"NO" is made in step S119. The program thus proceeds to step S128 formaking a discrimination as to whether MDN(ON)=3 or not, and a judgementof "YES" is made therein. At this time, the program proceeds to stepS129, in which a discrimination is made whether the time of lapse fromthe start of downshifting (TMST-TM) has reached a predetermined timeYTMDN4. If TMST-TM<YTMDN4, the program proceeds to step S123 andfollowing steps and the control in the synchronous mode is continued.

Once TMST-TM≧YTMDN4, the program proceeds to step S130, in which adiscrimination is made whether "Gratio" has fallen below that upperlimit value YG(N-1)H for judging the engagement of hydraulic clutchwhich is set based on the gear ratio of the speed stage to beestablished after speed changing. When "Gratio"≦YG(N-1)H, the programproceeds to step S131, in which, by using a timer value TMSTC which isset to a value of TM at the time when a condition of "Gratio"≦YG(N-1)Hhas been satisfied, a discrimination is made whether the time of lapsefrom the point of time when the condition of "Gratio"≦YG(N-1)H has beensatisfied (TMSTC-TM) has reached a predetermined time YTMDN5. Then, when"Gratio">YG(N-1)H or TMSTC-TM<YTMDN5, the program proceeds to step S123and following steps, and the control in the synchronous mode iscontinued. Once TMSTD-TM≧YTMDN5, the program proceeds to step S132 and adiscrimination is made whether FTBD=1 or not. If FTBD=0, a setting ofMDN(ON)=4 is made in step S133 and then QDNONC is set to an appropriatevalue in step S134 depending on the vehicle speed and the throttleopening. Further, in step S135, QDNOND is set to a value which isobtained by adding ΔQDNOND to the previous value of QDNOND. Then, instep Δ136, a discrimination is made whether "Gratio" lies within a rangeof the upper limit value YG(N-1)H and the lower limit value YG(N-1)L forjudging the engagement of hydraulic clutch, which values are set basedon the gear ratio of the speed stage to be established after speedchanging. If the result of this discrimination is "NO", TMSTD is set instep S137 to the value of TM at that time, and the program then proceedsto step S127. In this case, since QDNOND increases by ΔQDNOND by theoperation (or computation) in step S135, QDNON to be obtained in stepS127 also gradually increases, and the control of the ON pressure in theend mode is started.

In the next downshifting control processing, since the setting ofMDN(ON)=4 has already been made in step S133 last time, a judgement of"NO" is made in step S128. The program thus proceeds to step S132 andfollowing steps and the control in the end mode is continued. Then, whena judgement of "YES" is made in step S136, the program proceeds to stepS138. In this step, a discrimination is made whether the time in which"Gratio" continuously lies within the range of YG(N-1)H and YG(N-1)L,i.e., the time of duration of the condition of engagement completion ofthe hydraulic clutch on the engaging side (TMSTD-TM) has reached apredetermined time YTMDN6. Once TMSTD-TM≧YTMDN6, the program proceeds tostep S111 and a downshifting completion processing is performed.

If a judgement of FTB=1 is made in step S126 or S132, the programproceeds directly to step S111 and the downshifting completionprocessing is performed. The processing of setting FTBD is shown in FIG.27. During downshifting control processing to downshift to a speed stageof one lower speed stage G(N-1), if a downshifting command is issued todownshift to a still lower speed stage G(N-2) (S1201, S1202), a settingof FTBD=1 is made (S1203). In the cases other than the above, aresetting of FTBD=0 is made (S1204).

According to the above-described control, when "Gratio"≦YGDNS, the ONpressure rises by the transfer to the synchronous mode. There is,however, a response delay until the actual hydraulic pressure of thehydraulic clutch on the engaging side (hereinafter referred to as ONclutch pressure) rises. This response delay is short at a high vehiclespeed and long at a low vehicle speed due to the influence of acentrifugal force. Therefore, as shown in FIG. 13A, the followingarrangement is made. Namely, considering the difference between theresponse delay "a" at a low vehicle speed and a response delay b at ahigh vehicle speed, YGDNS is set relatively high at a low vehicle speedand is set relatively low at a high speed, so that at the time when"Gratio" has entered the synchronous region between YG(N-1)H andYG(N-1)L, the ON clutch pressure is boosted, regardless of the vehiclespeed, to a predetermined pressure at which no slipping in the hydraulicclutch occurs.

In addition, when the engine temperature is low, the output torque ofthe engine increases by a fast idle operation and, therefore, the speedof decrease in "Gratio" at the time of downshifting becomes larger thanat the time of high engine temperature, as shown in FIG. 13B. Therefore,the following arrangement is made. Namely, by detecting the enginetemperature, i.e., the engine cooling water temperature TW, YGDNS is sethigher at a low cooling water temperature than at a high cooling watertemperature, so that even at the time of low cooling water temperature,the ON clutch pressure is boosted, at the time when "Gratio" has enteredthe synchronous region, to a predetermined pressure at which no slippingin the hydraulic clutch occurs. The boosting response delay "a" of theON clutch pressure is constant irrespective of the engine temperature.In this embodiment, however, in order to enable to deal with thedifference in the boosting response delay in the ON clutch pressure dueto the vehicle speed, YGDNS is computed in step S104' from the map, forexample, with the vehicle speed and the cooling water temperature asparameters.

Details of operational processing of QDNOFF in step S108 are shown inFIG. 14. First, in step S108-1, a discrimination is made whetherMDN(OFF)=0 or not. Since MDN has been set to "0,0" in the firstdownshifting control processing, a judgement of "YES" is made in stepS108-1. The program thus proceeds to step S108-2, in which an initialvalue QDNOFFA of the OFF pressure in the initial pressure mode is set toan appropriate value depending on the vehicle speed and the throttleopening. Then, in step S108-3, a setting of MDN(OFF)=0 is made and, instep S108-4, a speed ratio "etr" of the torque converter 2 (rotationalspeed of input shaft 3/rotational speed of engine) at that time isstored in memory as "etrm". Then, the program proceeds to step S108-5,in which there is computed a boosting correction value QDNOFFZ. Thisboosting correction value QDNOFFZ varies with a degree of development(or progress) of speed change of the engine rotational speed at the timeof start of downshifting, which degree of development being dependent onan increase in the rotational speed of the engine due to slipping in thefluid torque converter 2. The value QDNOFFZ is computed by multiplying areference (standard) value QDNOFFZO depending on the throttle opening bya speed change developing degree function K which is obtained by afunctional operation with "etrm" as a parameter. The function K will bedescribed in detail hereinafter. When QDNOFFFZ has been computed, theprogram proceeds to step S108-6, in which QDNOFFB which is a value ofthe OFF pressure in a low pressure holding mode is set to a value whichis obtained by adding QDNOFFZ to a reference value QDNOFFBO depending onthe throttle opening. Then, in step S108-7, an annealing processing isperformed for gradually decreasing QDNOFFB from QDNOFFA down to a valueto be set as described above. Thereafter, in step S108-8, QDNOFF is setto QDNOFFB. In this manner, there is started a control in the initialpressure mode in which the OFF pressure is gradually decreased fromQDNOFFA.

In the next downshifting control processing, since the setting ofMDN(OFF)=1 has already been made in step S108-3 last time, a judgementof "NO" is made in step S108-1. The program thus proceeds to step S108-9for discriminating as to whether MDN(OFF)=1 or not and a judgement of"YES" is made therein. At this time, the program proceeds to stepS108-10, in which a discrimination is made whether "Gratio" has fallenbelow that lower limit value YG(N)L for judging the engagement of clutchwhich is set based on the gear ratio of the speed stage establishedbefore speed changing. If "Gratio">YG(N)L, a discrimination is made instep S108-11 whether the time of lapse from the start of downshifting(TMST-TM) has reached a predetermined time YTMDN7. While TMST-TM<YTMDN7,the program proceeds to step S108-3 and following steps, and the controlin the initial pressure mode is continued. When "Gratio"≦YG(N)L orTMST-TM≧YTMDN7, a setting of MDN(OFF)=2 is made in step S108-12 and theprogram proceeds to step S108-5 and following steps. A control of theOFF pressure in the low pressure holding mode is started.

In the next downshifting control processing, since the setting ofMDN(OFF)=2 has already been made last time in step S108-12 last time, ajudgement of "NO" is made in step S108-9. The program thus proceeds tostep S108-13 for making a judgement as to whether MDN(OFF)=2 or not, anda judgement of "YES" is made therein. At this time, the program proceedsto step S108-14, in which a discrimination is made whether "Gratio" hasfallen below a predetermined value YGDNT. If "Gratio">YGDNT, adiscrimination is made in step S108-15 whether a time of lapse from thestart of downshifting (TMST-TM) has reached a predetermined time YTMDN8.While TMST-TM<YTMDN8, the program proceeds to step S108-12 and followingsteps and the control in the low pressure holding mode is continued.Then, when "Gratio"≦YGDNT or TMST-TM≧YTMDN8, a setting of MDN(OFF)=3 ismade in step S108-16. The program then proceeds to step S108-17, inwhich a value QDNOFFC of the OFF pressure in the tail mode is set to anappropriate value depending on the throttle opening. Then, in stepS108-18, QDNOFF is set to QDNOFFC, and the control is started in thetail mode in which the OFF pressure is held in a lower pressure than inthe low pressure holding mode.

In the next downshifting control processing, since the setting ofMDN(OFF)=3 has already been made in step S108-16 last time, a judgementof "NO" is made in step S108-13. The program thus proceeds to stepS108-19 for making a discrimination as to whether MDN(OFF)=3 or not, anda judgement of "YES" is made therein. At this time, the program proceedsto step S108-20, in which a discrimination is made whether the time oflapse from the start of downshifting (TMST-TM) has reached apredetermined time YTMDN4. If TMST-TM≧YTMDN4, the program proceeds tostep S108-21, in which a discrimination is made whether "Gratio" hasfallen below YG(N-1)H or not. If TMST-TM<YTMDN4 or "Gratio">G(N-1)H, theprogram proceeds to step S108-16 and following steps, and the control inthe tail mode is continued. Then, when TMST-TM≧YTMDN4 and also when"Gratio"≦YG(N-1)H, the program proceeds to step S108-22, in which thevalue of TM at that time is set to TMSTC which is used in a timecounting processing in the above-described step S131. Then, in stepS108-23, a setting of MDN(OFF)=4 is made and also, in step S108-24, thevalue QDNOFFD of the OFF pressure in the end mode is set to a valuewhich gradually decreases from QDNOFFC. In step S108-25, QDNOFF is setto QDNOFFD, and the control of the OFF pressure in the end mode isperformed.

The above-described speed change developing degree function K isobtained as follows. Let a scheduled (or estimated) speed ratio of thefluid torque converter 2 at the time of downshifting completion be astandard (or reference) speed ratio Yetr. Let the rotational speed ofthe engine to be obtained by Yetr and the rotational speed Nin of theinput shaft 3 of the transmission at the time of starting thedownshifting be a standard (or reference) rotational speed of the engineNeG(N). And let the rotational speed of the engine at the time ofdownshifting completion which is obtained by NeG(N) and the speed changeratio YG(N) before starting the downshifting and the speed change ratioYG(N-1) after the completion of the downshifting be a target rotationalspeed of the engine NeG(N-1). Then, the speed change developing degreefunction K can be obtained by the following formula as a ratio of thedifference between NeG(N) and the actual rotational speed Ne of theengine at the time of starting the downshifting to the differencebetween NeG(N-1) and NeG(N).

    K=(Ne-NeG(N))/(NeG(N-1)-NeG(N))                            (1)

In other words, the speed change developing degree function K denotes aratio of an increase amount in the rotational speed of the engine due toslipping of the fluid torque converter 2 at the time of starting ofdownshifting, to the change amount in the rotational speed of the enginewhen downshifting is carried out while the speed ratio "etr" of thefluid torque converter 2 is held at Yetr.

Here, NeG(N) and NeG(N-1) are respectively expressed as follows.##EQU1## Ne can be expressed as

    Ne=Nin/etrm                                                (4)

where etrm is an actual etr at the time of starting of downshifting. Ifrearrangement is made by substituting formulas (2), (3), and (4) intoformula (1), the following is obtained.

    K={(Yetr/etrm-1)}/{(YG(N-1)/YG(N)-1)}                      (5)

When the accelerator pedal is stepped slowly, if the vehicle speed doesnot change, only the rotational speed of the engine increases due toslipping in the fluid torque converter 2, with the result thatrotational speed of the engine sometimes exceeds NeG(N) at the time ofstarting of downshifting. In such a case, when slipping occurs to thehydraulic clutch on the disengaging side after the starting ofdownshifting, the rotational speed of the input shaft 3 rapidlyincreases so as to approach the rotational speed of the engine that hasalready been increased, and the speed of decrease in "Gratio" becomeslarge. As a result, while the ON clutch pressure has not risensufficiently, "Gratio" enters into the synchronous region, and thehydraulic clutch on the engaging side therefore can no longer be engagedat the time of synchronization. Therefore, in the present embodiment,the following arrangement is employed. Namely, the boosting correctionvalue QDNOFFZ is operated (or computed) by using the speed changedeveloping degree function K to be obtained by formula (5) with "etrm"as a parameter, and the value QDNOFFB is added by the amount of QDNOFFZ.The decrease in "Gratio" is thereby restrained by the engaging force ofthe hydraulic clutch on the disengaging side so that the hydraulicclutch on the engaging side can be sufficiently engaged at the time ofsynchronization. Since "etr" at the time of completion of speed changevaries delicately with the operating conditions of the engine, it ispreferable to replace the value of Yetr to be substituted into formula(5) depending on the operating conditions of the engine.

Further, in the present embodiment, if the speed stage designationsignal SH is switched (or changed), during downshifting control fromG(N) to G(N-1), to a signal to designate a speed stage which is a stilllower speed stage G(N-2) to thereby make a setting of FTBD=1, adownshifting completion processing is performed when the control of theON pressure in the low pressure correction mode has been completed (whenthe control in a synchronous mode has been completed when a setting ofFTBD=1 is made during the control of the ON pressure in the synchronousmode), whereby the downshifting control from G(N-1) to G(N-2) isstarted. Since the downshifting control from G(N) to G(N-1) is completedin this manner at an early time, the time required for the downshiftingfrom G(N) to G(N-2) is shortened, resulting in an improved drivability.

There is a case where, during downshifting control from G(N) to G(N-1),the speed change designation signal SH is switched or changed to asignal designating G(N) or a case where, during upshifting control fromG(N) to G(N+1), the speed change designation signal SH is switched to asignal designating G(N). In such a case, the hydraulic pressure of thehydraulic clutch relating to the speed changing can be controlled withthe first and the second solenoid proportional valves 17₁, 17₂ evenwithout switching the position of the first and the second shift valves12₁, 12₂ or the changeover valve 13.

For this purpose, the following arrangement is made. Namely, when thespeed change designation signal SH is switched to a signal designatingG(N) during downshifting control from G(N) to G(N-1), the downshiftingcontrol is stopped on the way (or in the course of the control), and aswitchover upshifting to switch (or transfer) to an upshifting controlfrom G(N-1) to G(N) is performed. When the speed change designationsignal SH is switched to a signal designating G(N) during upshiftingcontrol from G(N) to G(N+1), the upshifting control is stopped on theway, and a switchover downshifting to switch to a downshifting controlfrom G(N+1) to G(N) is performed.

Details of switchover upshifting control are shown in FIG. 16. Anexplanation will now be made with reference to FIG. 15 whichschematically shows the changes of the ON pressure, the OFF pressure,and the "Gratio", respectively. First, in step S201, MUP is set to "4,4"and MDN is reset to "0,0". Then, in step S202, TM is set to TMST.Thereafter, in step S203, a discrimination is made whether the time oflapse from the start of upshifting (TMST-TM) has reached a predeterminedtime YTMUP1. Once TMST-TM≧YTMUP1, the program proceeds to step S204, inwhich the upshifting completion processing is performed. The contents ofthis processing are the same as those in step S13 shown in FIG. 7.

If TMST-TM<YTMUP1, the value QUPONB of the ON pressure in the bottom upmode in upshifting is computed in step S205. Then, in step S206, adiscrimination is made whether MUP(ON)=4 or not. In the firstprocessing, a judgement of "YES" is made in step S206, and the programproceeds to step S207, in which a discrimination is made whether"Gratio" has exceeded YGUPT or not. If "Gratio"<YGUPT, there isperformed in step S208 an annealing processing in which QUPONB isgradually changed from the final value of QDNOFF in the precedingdownshifting control to the value of QUPONB that was obtained in stepS205. In step S209, QUPON is set to QUPONB and, in step S210, anoperational processing of QUPOFF is performed. Then, in step S211, theproportional valve selection processing is performed. The operationalprocessing of QUPOFF is performed in the same manner as in theprocessing in steps S10-16 through S10-19 in FIG. 9. The proportionalvalve selection processing is the same as the processing in step S11 inFIG. 7.

Once "Gratio"≧YGUPT, MUP is set to "5,5" in step S212 and, in step S213,TMSTB is set to the value of TM at that time. Then, in step S214, QUPONis set to a value which is obtained by adding QUPONC to QUPONB. Since aninitial value of QUPONC is zero, a condition of QUPON=QUPONB occurs, andthe control of the ON pressure in the bottom up mode is performed.

In the next processing, since MUP has already been set to "5,5" in stepS212 last time, a judgement of "NO" is made in step S206. The programproceeds to step S215 for making a discrimination as to whetherMUP(ON)=5 or not, and a judgement of "YES" is made therein. At thistime, a discrimination is made in step S216 whether "Gratio" hasexceeded YG(N)L or not. While "Gratio"<YG(N)L, the program proceeds tostep S212 and following steps, and a control of the ON pressure in thebottom up mode is continued. Once "Gratio"≧YG(N)L, MUP is set to "7,7"in step S217, and the program proceeds to step S218 and following steps.Therefore, in the next processing, a judgement of "NO" is made in stepS215, and the program proceeds directly to step S217. In step S218, aprocessing is made to set QUPONC to a value which is obtained by addingΔQUPONC to the previous value of QUPONC. Then, in step S219, adiscrimination is made whether "Gratio" has fallen within a rangebetween YG(N)L and YG(N)H. If the result of this discrimination is "NO",the program proceeds to step S213 and following steps. In this case,since QUPONC increases by ΔQUPONC by the operation (or computation) instep S218, QUPON to be obtained in step S214 also gradually increases,and a control of the ON pressure in the end mode is performed. IfYG(N)L≦"Gratio"≦YG(N)H, i.e., if the hydraulic clutch on the engagingside is in a condition of completion of engagement, a discrimination ismade in step S220 whether the time of duration of the condition ofcompletion of engagement (TMSTB-TM) has reached a predetermined timeYTMUP6 or not. When TMSTB-TM≧YTMUP6, the program proceeds to step S204,in which the upshifting completion control is performed.

Details of the switchover downshifting are shown in FIG. 18. Anexplanation will now be made with reference to FIG. 17 whichschematically shows the changes in the ON pressure, the OFF pressure,and the "Gratio", respectively. First, in step S301, MUP is reset to"0,0" and MDN is set to "2,2". Then, in step S302, TM is set to TMSTand, in step S303, a discrimination is made whether the time of lapsefrom the starting of downshifting (TMST-TM) has reached a predeterminedtime YTMDN1. Once TMST-TM≧YTMDN1, the program proceeds to step S304, inwhich the downshifting completion processing is performed. The contentsof this processing are the same as those of step S111 shown in FIG. 12.

If TMST-TM<YTMDN1, a discrimination is made in step S305 whetherMDN(ON)=2 or not. In the first processing, a judgement of "YES" is madein step S305, and the program proceeds to step S306, in which adiscrimination is made whether "Gratio" has exceeded YGDNS or not. If"Gratio">YGDNS, QDNONB is computed in step S307. In step S308, there isperformed an annealing processing in which QDNONB is gradually changedfrom the final value of QUPOFF in the previous upshifting control to thevalue of QDNONB that was obtained in step S307. In step S309, QDNON isset to QDNONB and then, in step S310, an operational processing ofQDNOFF is performed. Then, in step S311, the proportional valveselection processing is performed. The control of the ON pressure in thelow pressure correction mode is thereby performed. The operationalprocessing of QDNOFF is performed in a similar manner to that of stepS108-13 and following steps in FIG. 14 in a mode in which the steps ofS108-15 and S108-20 are omitted therefrom. The proportional valveselection processing is the same as the processing in step S109 shown inFIG. 12.

Once "Gratio"≦YGDNS, MDN is set to "3,3" in step S312 and in step S313,QDNOC is computed. Then, in step S314, there is performed an annealingprocessing in which QDNONC is gradually changed from the final value ofQDNONB to the value that was obtained in step S312. Then, in step S315,QDNON is set to a value which is obtained by adding QDNOND to QDNONC.Since an initial value of QDOND is zero, a condition of QDNONC=QDNONoccurs, and the control of the ON pressure in the synchronous mode isstarted.

In the next processing, since MDN has already been set to "3,3" in stepS312 last time, a judgement of "NO" is made in step S305. The programthus proceeds to step S316 for discriminating whether MDN(ON)=3 or not,and a judgement of "YES" is made therein. At this time, a discriminationis made in step S317 whether "Gratio" has fallen below YG(N)H or not. If"Gratio"≦YG(N)H, the program proceeds to step S318, in which adiscrimination is made whether the time of lapse from the time when thecondition of "Gratio"≦YG(N)H has been satisfied (TMSTC-TM) has reached apredetermined time YTMDN5. If "Gratio">YG(N)H or TMSTC-TM<YTMDN5, theprogram proceeds to step S313 and following steps, and the control inthe synchronous mode is continued.

Once TMSTC-TM≧YTMDN5, a setting of MDN(ON)=4 is made in step S319. Then,in step S320, QDMONC is computed and in step S321, QDNOND is set to avalue which is obtained by adding ΔQDNOND to the previous value ofQDNOND. Then, in step S322, a discrimination is made whether "Gratio"lies within a range between YG(N)L and YG(N)H. If the result of thisdiscrimination is "NO", TMSTD is set in step S323 to a value of TM atthat time, and the program then proceeds to step S315. In this case,since QDNOND increases by ΔQDNOND by the operation in step S321, thevalue QDNON to be obtained in step S315 also gradually increases, andthe control of the ON pressure in the end mode is performed. If ajudgement of "YES" is made in step S322, a discrimination is made instep S324 whether the time of duration of the condition of engagement ofthe hydraulic clutch on the engaging side (TMSTD-TM) has reached apredetermined time YTMDN6. When TMSTD-TM≧YTMDN6, the program proceeds tostep S304, in which the downshifting completion processing is performed.

As described above, in the switchover upshifting control or switchoverdownshifting control, it is only when a discrimination is made as towhether or not the speed change time has reached YTMUP1, YTMDN1 whichserve as a basis for discriminating an abnormality that a discriminationis made based on the time of lapse from the start of speed changing(TMST-TM). This is because the switchover speed changing is started inthe midst of the previous speed changing and, therefore, the conditionof speed change development can no longer be judged from the time oflapse from the start of speed changing. Consequently, the condition ofthe speed change development must be judged only from "Gratio". And,once "Gratio" can no longer be accurately detected due to troubles insensors, or the like, it becomes impossible to adequately control the ONpressure or the OFF pressure depending on the condition of speed changedevelopment. As a solution, by using a flag FGFAIL which is set to "1"when "Gratio" can no longer be detected accurately, the switchover speedchanging is prohibited when FGFAIL=1. Further, in the forward runningranges such as "D₄ ", "D₃ ", etc., the speed changing is performedaccording to a speed change map which is set with the vehicle speed andthe throttle opening as parameters. Here, the vehicle speed sensor 22detects the vehicle speed based not on the absolute speed but on therotational speed of the wheels. Therefore, when tire locking hasoccurred due to braking on a low-μ road or the like, the vehicle speed Vto be detected by the vehicle speed sensor 22 lowers down to nearly zerowhile the actual vehicle speed makes little or no change. Downshiftingis thus performed according to the speed change map, and upshifting isperformed depending on the vehicle speed after the gripping of the tireshas recovered. This results in an unnecessary speed changing. Inaddition, in the condition of manual speed changing in which speedchanging of one speed stage at a time is performed by the operation ofthe lever, downshifting to the first speed stage is automaticallyperformed when the vehicle speed becomes extremely low so that thevehicle can start again in the first speed stage after stopping.Upshifting is then performed by a subsequent lever operation. Therefore,once downshifting to the first speed stage has been performed due tolocking of tires, the first speed stage remains to be established evenafter the tire gripping has been recovered. This will force the driverto perform upshifting to a speed stage that suits the vehicle speed. Inorder to eliminate this kind of disadvantage, the following arrangementis employed. Namely, when the vehicle speed to be detected by thevehicle speed sensor 22 has suddenly decelerated due to locking oftires, i.e., when the vehicle speed has decreased at a decelerationabove a predetermined value, a flag FLOCK which is set to "1" for apredetermined period of time is used to thereby prohibit downshiftingwhen FLOCK=1.

FIG. 19 shows shift selection processing using FGFAIL and FLOCK. In thisprocessing, a discrimination is made first in step S401 as to whetherthe speed stage G(SH) to be designated by the speed stage designatingsignal SH is the same as the speed stage G(SHO) that has been designatedso far. If G(SH)≠G(SHO), a discrimination is made in step S402 whetherG(SH) is of a higher speed stage than G(SHO). If G(SH)>G(SHO), theupshifting flag FUP is set to "1" in step S403. If G(SH)<G(SHO), adiscrimination is made in step S404 whether FLOCK=1 or not. If FLOCK=0,FUP is reset to "0" in step S405. Then, a discrimination is made in stepS406 as to whether MAT is set to "A,B" or not, i.e., whether the controlfor speed changing is going on or not. If MAT=A,B, a switchover speedchange flag FCS is set to "1" in step S407. If MAT≠A,B, FCS is reset to"0" in step S408. Then, in step S409, a discrimination is made as towhether FCS=1 or not. If FCS=0, a discrimination is made in step S410whether FUP=1 or not. If FUP=1, the program proceeds to step S411 toperform upshifting control. If FUP=0, the program proceeds to step S412to perform downshifting control. If FCS=1, a discrimination is made instep S413 whether FGFAIL=1 or not. If FGFAIL=0, a discrimination is madein step S414 whether FUP=1 or not. If FUP=1, a switchover upshiftingcontrol is performed in step S415. If FUP=0, a switchover downshiftingcontrol is performed in step S416. If FGFAIL=1, the processing isterminated or ended to prohibit the switchover speed changing. When adiscrimination of FLOCK=1 is made in step S404, the processing is alsodirectly ended to prohibit downshifting. Since FLOCK is reset to "0"after a predetermined period of time, it is only during thepredetermined period of time after the occurrence of locking of tiresthat the downshifting is prohibited. Thereafter, downshifting is allowedin preparation for stopping of the vehicle.

In the setting processing of FGFAIL, there is used a timer value TMG(N)which is obtained by counting the time during which "Gratio" liesbetween those lower limit value YG(N)L and upper limit value YG(N)H forjudging the engagement of hydraulic clutch which are set based on thegear ratio of the speed stage G(N) that has been established at the timeof non-speed changing. TMG(N) is prepared for each of the speed stages.As shown in FIG. 20A, a discrimination is made first in step S1100 as towhether MAT is set to "A,0" or "0,B", i.e., whether it is in anon-speed-change time. If it is in non-speed-change time, adiscrimination is made in step S1101 whether "Gratio" falls within arange between the upper and lower limit values YG(N)L, YG(N)H of thefirst speed stage. If it falls within this range, a timer value TMG(1)for the first speed stage is added in step S1102. If it falls outsidethe above-described range, TMG(1) is subtracted in step S1103. Then,similar processings are performed in steps S1104, S1105, S1106 for thesecond speed stage, in steps S1107, S1108, S1109 for the third speedstage, in steps S1110, S1111, S1112 for the fourth speed stage, and insteps S1113, S1114, S1115 for the reverse running stage to therebyperform adding or subtracting processing of timer values TMG(2), TMG(3),TMG(4), and TMG(R) for the second speed stage through fourth speed stageand the reverse running stage. Therefore, each of these timer valuesTMG(1)-TMG(R) becomes a difference between the accumulated time at which"Gratio" falls within the corresponding range of upper and lower limitvalues YG(1)L, YG(1)H through YG(R)L, YG(R)H and the accumulated time atwhich "Gratio" falls outside this range. If the detection of "Gratio" isaccurate, the timer value TMG(N) for the speed stage G(N) that has beenestablished right before the speed changing prior to the switchoverspeed changing will become a large enough value. Therefore, as shown inFIG. 20B, a comparison is made in step S1116 between TMG(N) and apredetermined threshold value YTMG. When TMG(N)>YTMG, setting ofFGFAIL=0 is made in step S1117 and, when TMG(N)≦YTMG, setting ofFGFAIL=1 is made in step S1118.

As shown in FIG. 21A, there is measured the time t for the vehicle speedV which is detected by the vehicle speed sensor 22 to decrease from afirst predetermined vehicle speed YVH (e.g, 40 km/h) which is setrelatively high down to a second predetermined vehicle speed YVL (e.g.,10 km/h) which is set relatively low. When this time t has fallen belowa predetermined value, FLOCK is set to "1" for a predetermined period oftime. This predetermined value is set, for example, such that(YVH-YVL)/t becomes about 1G (the acceleration of gravity). Details ofsetting processing of FLOCK are shown in FIG. 21B. First, in step S1001,a discrimination is made whether the vehicle speed V has fallen belowYVH. If V≧YVH, the program proceeds to step S1002, in which theremaining time tm of a subtractive timer which is different from theabove-described timer for speed change control is set to an initialvalue of tmst. Then, in step S1003, a resetting of FLOCK=0 is made. IfV<YVH, a discrimination is made in step S1004 whether the vehicle speedV has fallen below YVL. If V≧YVL, the program proceeds to step S1003.When V≦YVL, the program proceeds to step S1005 for discriminatingwhether FLOCK=1 or not. If FLOCK=0, a discrimination is made in stepS1006 whether the time t required for the vehicle speed V to lower fromYVH to YVL (tmst-tm) has fallen below a predetermined time Ytmlock. Iftmst-tm≦Ytmlock, a discrimination is made in step S1007 whether tm hasbecome zero (whether a time tmst has elapsed from the condition V<YVHhas been satisfied). If tm≠0, a setting of FLOCK=1 is made in stepS1008. From the next time, as long as V<VHL, the program proceeds fromstep S1005 to step S1008 and is held to FLOCK=1 for a predeterminedperiod of time until a condition of tm=0 (tmst-Ytmlock) is satisfied.This predetermined period of time is set a little longer, e.g., forabout 10 seconds, than the braking time in case a temporary brake isapplied without an intention of parking.

Details of in-gear control are shown in FIG. 23. An explanation will nowbe made with reference to FIG. 22 which schematically shows the changesin the ON pressure and the "Gratio" at the time of gear engagement (orgear-in). In the in-gear control, a discrimination is made first, instep S501, whether MAT is set to one of "2,0", "4,0", and "6,0". In thefirst processing, a judgement of "NO" is made in step S501. In stepS502, TM is set to TMST and, in step S503, QINGA which is a value of theON pressure in the response pressure mode is set to an appropriate valuedepending on the throttle opening. The value QINGA decreases with thelapse of time. Then, in step S504, MAT is set to "2,0" and thereafter,in step S505, QING which is a command value of the ON pressure in thein-gear control is set to QINGA. Then, the program proceeds to stepS506, in which the proportional valve selection processing is performed.In this processing, the command value of the output pressure of that oneof the first and the second solenoid proportional valves 17₁, 17₂ whichcontrols the hydraulic pressure of the hydraulic clutch to be engaged atthe time of gearing in is made to be QING, and the command value of theoutput pressure of the other thereof is made to be atmospheric.

In the next processing, since MAT has already been set to "2,0" in stepS504 last time, a judgement of "YES" is made in step S501. The programthus proceeds to step S507, in which a discrimination is made whether ornot the time of lapse from the start of gear engagement (TMST-TM) hasreached a limit value YTMING1 for judging the presence or absence ofabnormality. When TMST-TM≧YTMING1, the program proceeds to step S508, inwhich an in-gear completion processing is performed. In this processing,MAT is set to "A,0" (at the time of gear-in to the first speed stage,third speed stage, and reverse stage), or to "0,B" (at the time ofgear-in to the second speed stage) and also TM is reset to zero. IfTMST-TM<YTMING1, the program proceeds to step S509 for discriminatingwhether MAT has been set to "2,0" or not, and a judgement of "YES" ismade therein. At this time, the program proceeds to step S510, in whicha discrimination is made whether the time of lapse from the start ofgear-in has reached a predetermined time YTMING2. While TMST-TM<YTMING2,the program proceeds to step 503 and following steps, and a control inthe response pressure mode is performed.

Once TMST-TM>YTMING2, the program proceeds to step S511, and MAT is setto "4,0". Then, in step S512, a discrimination is made whether "Gratio"has exceeded a predetermined value YGINGS or not. When "Gratio"<YGINGS,a flag FING is set to "1" in step S513 and further, in step S514, thevalue of TM at that time is stored in memory as TMD. Then, in step S515,ΔQINGX is set to a relatively large value. Once the hydraulic clutchbegins to be engaged and the condition of "Gratio"≧YGINGS is satisfied,a discrimination is made in step S516 whether FING=1 or not. If FING=0,the program proceeds to step S515. If FING=1, the program proceeds toS517, in which a discrimination is made whether the time required forthe condition of "Gratio"≧YGINGS to be satisfied from the start ofgear-in (TMST-TMD) has exceeded a predetermined time YTMING3. Then, ifTMST-TMD<YTMING3, ΔQINGX is set in step S518 to a relatively smallvalue. If TMST-TMD≧YTMING3, ΔQINGX is set in step S519 to anintermediate value. Once ΔQINGX has been set in this manner, the programproceeds to step S520, in which QINGX is set to a value which isobtained by adding ΔQINGX to the previous value of QINGX. Then, in stepS521, the value QINGB of the ON pressure in the addition mode is set toa value which is obtained by adding QINGX to the final value of QINGA.And in step S522, QING is set to QINGB. Since MAT has already been setto "4,0" last time in step S511, a judgement of "NO" is made in stepS509. The program proceeds to step S523 for discriminating whether MAThas been set to "4,0" or not, and a judgement of "YES" is made therein.At this time, the program proceeds to step S524, in which adiscrimination is made whether "Gratio" has exceeded that lower limitvalue YG(N)L for judgement of the clutch engagement which is set basedon the gear ratio of the speed stage to be established at the time ofgear-in. While "Gratio"<YG(N)L, the program proceeds to step S511 andfollowing steps, and the control in the addition mode is performed.

When "Gratio"≧YG(N)L, the program proceeds to step S525, and MAT is setto "6,0". From the next time, a judgement of "NO" is made in step S523,and the program proceeds directly to step S525. Then, the programproceeds to step S526, in which a discrimination is made whether or not"Gratio"≧YG(N)L or not. If "Gratio"<YG(N)L, the value of TM at that timeis stored in memory as TMSTE in step S527, and the program then proceedsto step S528. If "Gratio"≧YG(N)L, the program proceeds directly to stepS528. In step S528, QINGC is set to a value which is obtained by addingΔQINGC to the previous value of QINGC. Then, the program proceeds tostep S529, in which a discrimination is made whether the time ofduration of the condition of "Gratio"≧YG(N)L, i.e., the condition ofclutch engagement completion (TMSTE-TM) has reached a predetermined timeYTMING4. Then, while TMSTE-TM<YTMING4, the program proceeds to stepS530, in which QING is set to a value which is obtained by adding QINGCto the final value of QINGB, and the control of the ON pressure in theend mode is performed. Once TMSTE-TM≧YTMING4, the program proceeds tostep S508, and the in-gear completion processing is performed.

According to the above-described control, since ΔQINGX is set to a largevalue until the condition of "Gratio" >YGINGS has been attained in anin-gear mode, the boosting speed of the ON pressure becomes large.Thereafter, the boosting speed of the ON pressure becomes small.Therefore, it becomes possible to shorten the time lag at the time ofgear-in, and also to prevent the in-gear shocks. In addition, in acondition in which the hydraulic pressure is likely to lower due to ahigh temperature or the like, it takes time for the hydraulic clutch tostart engagement. Under this kind of conditions, if the boosting speedof the ON pressure from the time when the condition of "Gratio"≧YGINGShas been satisfied is made small, it take time for the hydraulic clutchto complete engagement, resulting in a large time lag. In the presentembodiment, on the other hand, if it takes time to the start ofengagement of the hydraulic clutch, the condition becomesTMST-TMD≧YTMING3, and ΔQINGX is set to an intermediate value. Therefore,the boosting speed of the ON pressure after the condition has become"Gratio"≧YGINGS does not lower so much, with the result that the timelag can be shortened.

If a switching is made to the forward range such as "D₄ " or the likewhile the vehicle is running in the reverse range "R", "Gratio"sometimes remains to exceed YGINGS. The reason is as follows. Namely,"Gratio" is obtained by Nout/Nin, and the rotational speed of the outputshaft 7 is zero while the vehicle is stopped. If the rotational speed ofthe output shaft is made to be Nout as it is, "Gratio" will remain to bezero even if Nin lowers as a result of lowering of the rotational speedof the engine at the time of gear-in. As a solution, Nout is set to avalue obtained by adding a predetermined level-up value to therotational speed of the output shaft so that "Gratio" can increase as aresult of lowering of Nin. When a switchover is made from "R" range tothe forward range, the output shaft 7 is switched from the condition ofrotating in the reverse direction to the condition of rotating in thenormal direction. The rotational speed of the output shaft once becomeszero in the course of this switching but, since Nout has been levelledup as described above, the condition sometimes remains to be"Gratio"≧YGINGS. At the time of switching from the "R" range to theforward range, it is desired to accelerate the boosting of the ONpressure so that the output shaft 7 can be switched at an early stage tothe condition of rotating in the normal direction. In the presentembodiment, if the condition remains to be "Gratio"≧YGINGS, FING becomeszero (FING=0). The value ΔQINGX is thus maintained in a large value,whereby the above desire can be met.

Further, if a high speed stage which suits a high vehicle speed isestablished according to the speed change map when switching is made tothe forward range such as "D₄ " or the like while running at a highspeed in the "R" range, the transmission torque to the output shaft 7becomes small, and it takes time before the direction of rotation of theoutput shaft 7 is switched. During that time, the hydraulic clutch keepson slipping, and the durability of the hydraulic clutch is deteriorated.In such a case, the above-described disadvantage can be eliminated bymaking the following arrangement. Namely, by providing a vehicle speedsensor that can discriminate the direction of rotation of the wheels, orby providing a similar means, a discrimination is made whether therunning direction of the vehicle is forward or reverse. If the vehicleis discriminated to be running in the reverse direction in the forwardrange, a speed stage that is lower than usual is established. FIG. 24shows the control for that purpose. If a discrimination is made in stepS601 that the transmission is in the forward range, a discrimination ismade in step S602 whether the vehicle is running in the reversedirection or not. If the result of this discrimination is "NO", anordinary speed change map is selected as the speed change map in stepS603. If the vehicle is discriminated to be running in the reversedirection, a speed change map in which a measure is taken against thereverse running (also called a reverse-running-measure speed change map)is selected as the speed change map. The reverse-running-measure speedchange map is set, for example, such that the second speed stage or thefirst speed stage is established when, in an ordinary speed change map,the third speed stage or the second speed stage will be established,respectively.

If there is provided a means for detecting the forward or reverserunning such as a vehicle speed sensor equipped with a function fordiscriminating the direction of rotation, the cost becomes high.Therefore, without using a special sensor, the selection of the speedchange map at the time of switching from the "R" range to the forwardrange may be made by performing the following control. This control isperformed by using a flag FREV which is set to, and maintained at, "1"when the vehicle speed exceeds a predetermined value in the "R" range,and also when the vehicle speed never falls below a predetermined valuein the "N" range. Details of this control are shown in FIG. 25A. If adiscrimination is made in step S701 that the range is in the forwardrange, a discrimination is made in step S702 whether FREV=1 or not. IfFREV=0, an ordinary speed change map is selected as the speed change mapin step S703. If FREV=1, a reverse-running-measure speed change mapwhich is similar to the one mentioned hereinabove is selected in stepS704. Then, in step S705, a discrimination is made whether MAT is set toany one of "2,0", "4,0", and "6,0". When the result of thisdiscrimination becomes "NO", i.e., when the in-gear control has beencompleted, FREV is reset to "0" in step S706 and, from the next time, anordinary speed change map is selected. Details of the setting processingof FREV are shown in FIG. 25B. When the range is discriminated to be "R"range in step S801, a discrimination is made in step S802 whether thereverse transmission train GR has been established or not. If it hasbeen established, a discrimination is made in step S803 whether or notthe vehicle speed V has exceeded a predetermined value YVa (e.g., 10km/h). If V>YVa, FREV is set to "1" in step S804. Then, if the range isdiscriminated to be "N" range in step S805, a discrimination is made instep S806 whether the vehicle speed V has fallen below the predeterminedvalue YVa. When V<YVa, FREV is reset to "0" in step S807. According tothis arrangement, if FREV is set to "1" by satisfying the condition ofV>YVa in "R" range, the condition of FREV=1 is maintained unless thecondition becomes V<YVa in "N" range. Therefore, when a switchover ismade from "R" range to the forward range via "N" range, it can bediscriminated that the vehicle is in the reverse running if FREV=1. Itfollows that, during the reverse running in the forward range, thereverse-running-measure speed change map is selected, and the switchingfrom the reverse running condition to the forward running condition canbe accelerated. As a consequence, the durability of the hydraulicclutches can be improved. If an arrangement is made such that, at thetime of switching from the forward range to "R" range, the reverse speedstage GR is established when the vehicle speed has fallen below thepredetermined value as described above, it cannot make a hastyconclusion that the vehicle is running in the reverse direction even ifV>YVa in "R" range. Therefore, in the present embodiment, the followingarrangement has been made to prevent a misjudgment. Namely, a setting ofFREV=1 is made only when V>YVa in a condition in which the reverse speedstage GR is established in "R" range, and a setting of FREV=1 is notmade when the reverse speed stage GR is not established in the "R"range.

There is a case in which, while the vehicle is running, the electroniccontrol unit (ECU) 20 temporarily fails due to voltage drop and, oncethe voltage is up or restored, ECU20 is re-started after initializationoperation. During the failure of ECU20, the electric power supply to allthe solenoid valves is stopped, and the first and the second shiftvalves 12₁, 12₂ and the changeover valve 13 are switched to the leftposition, whereby the fourth speed stage is established. Further, evenif ECU20 is re-started, parameter values such as the vehicle speed,throttle opening, or the like cannot be read out during theinitialization of ECU20. Therefore, the speed stage according to thespeed change map cannot be designated. Therefore, conventionally, it isso arranged that a high speed stage is established during theinitialization (to prevent the engine overrotation by the establishmentof a low speed stage while running at a high speed) and that, aftercompletion of initialization, the speed changing is made to a speedstage according to the speed change map. In this system, however, whenECU20 fails while the vehicle is running at a low speed stage, therotational speed of the engine lowers due to establishment of a highspeed stage until the completion of initialization. Consequently, at thetime of downshifting to the low speed stage after completion ofinitialization, it becomes necessary to largely increase the rotationalspeed of the engine. Much time is therefore required for downshifting,and the restoration of the driving force is delayed.

As a solution, in the hydraulic oil circuit in the present embodiment,an arrangement is made such that the transmission can be made to aneutral condition even when the manual valve 11 has been switched to therunning range such as "R", "D₄ ", "D₃ ", "2", "1". Namely, if the firstand the second shift valves 12₁, 12₂ and the changeover valve 13 are inthe condition of speed changing, and if the output pressures of thefirst and the second solenoid proportional valves 17₁, 17₂ are in theatmospheric pressure, the hydraulic pressure in any of the hydraulicclutches C1-C4 also becomes atmospheric, with the result that thetransmission becomes neutral. Then, when ECU20 has been re-started, adiscrimination is made in step S901 whether initialization has beencompleted or not as shown in FIG. 26. While the initialization is goingon, a neutral signal is outputted in step S902, and a flag FINT is setto "1" in step S903. The neutral signal makes the first and the secondshift valves 12₁, 12₂ and the changeover valve 13 to a condition ofspeed changing, e.g., to a speed changing condition of third speedfourth speed in which the first and the second shift valves 12₁, 12₂ arein the left position and the changeover valve 13 is in the rightposition, and also in which the output pressures of both the first andthe second solenoid proportional valves 17₁, 17₂ are made to beatmospheric, whereby the transmission becomes the neutral condition.When the initialization has been completed, the program proceeds to stepS904, in which a discrimination is made whether FINT=1 or not. SinceFINT=1 right after the completion of the initialization, a judgement of"YES" is made in step S904. At this time, the program proceeds to stepS905, in which a discrimination is made whether the range is in therunning range or not. If it is not in the running range, i.e., if it isin "N" or "P" range, FINT is reset to "0" in step S906, and the programproceeds to step S907 to perform an ordinary control. The processing atthe time of starting of ECU20 by switching on the ignition key isperformed by this route. When it is in the running range, the programproceeds to step S908, and the in-gear control to establish the speedstage according to the speed change map is started. Then, in step S909,a discrimination is made whether MAT is set to one of "2,0", "4,0" and"6,0". If the result of this discrimination has become "No", i.e., whenthe in-gear control has been completed, FINT is reset to "0" in stepS910. In this manner, after the completion of the in-gear control, ajudgement of "NO" is made in step S904, and an ordinary control isperformed. According to this arrangement, even if the fourth speed stageis established by the failure in ECU20 while the vehicle is running in alow speed stage, the neutral condition is maintained, once ECU20 isre-started, until the initialization is completed. Therefore, duringthat period of time, the rotational speed of the engine increases, andthe gear-in to a lower speed stage after the completion of theinitialization is made in good response, resulting in an early recoveryof the driving force.

It is readily apparent that the above-described control apparatus for anautomatic vehicular transmission meets all of the objects mentionedabove and also has the advantage of wide commercial utility. It shouldbe understood that the specific form of the invention hereinabovedescribed is intended to be representative only, as certainmodifications within the scope of these teachings will be apparent tothose skilled in the art.

Accordingly, reference should be made to the following claims indetermining the full scope of the invention.

What is claimed is:
 1. A control apparatus for an automatic vehiculartransmission having a hydraulic engaging element to be engaged at a timeof gear-in by a switching operation from a neutral range to a runningrange, wherein a pressure of hydraulic oil to be supplied to saidhydraulic engaging element at the time of gear-in is defined to be anin-gear pressure, said apparatus comprising:means for detecting an inputand output speed ratio of the transmission; and means for lowering arate of increase of said in-gear pressure after said input and outputspeed ratio has exceeded a predetermined value which serves as a basisfor discriminating a start of engagement of said hydraulic engagingelement, wherein a degree of lowering of the rate of increase of saidin-gear pressure is variable depending on a time taken for said inputand output speed ratio to exceed said predetermined value after a startof gear-in.
 2. The control apparatus according to claim 1, wherein saidmeans for lowering a rate of increase of said in-gear pressure isoperated only when said input and output speed ratio has exceeded saidpredetermined value from a value smaller than said predetermined value.